A bit too vague, apparently.

Rob types the rule.
He suddenly feels incredibly anxious. He's about to change the body of an actual person.
Sure, the person is Aileen who had been brought into existence only earlier this morning, but she's still sitting right across from him.

He types fast, as if to make sure that Aileen can't change her mind before he's finished:

7. Aileen's body is human in all the ways that Aileen wants it to be.

Before confirming it, Rob slowly turns the phone to Aileen. Before he can show her what he'd written however, she stops him, grasping his hand.
"Don't show me. It felt nice being surprised by the rule you wrote on the beach. I want to experience the rule coming into existence from the inside again, without knowing beforehand."

Rob hesitates. "Are you sure? When I click to confirm it'll be here for good. No take backsies, like you said."
Aileen nods and smiles encouragingly. "I trust you. It's a two player game after all." She winks at him and Rob blushes at her reference to their earlier sexual encounter.

He clicks to confirm the rule. A green light blinks at the top right of his screen and his eyes immediately jump down to where the rules are written.
With the new addition, the rules now read like this:

1. THE APP "ABSOLUTE RULES" ALWAYS SHOWS INSTRUCTIONS ON HOW TO USE IT.
2. WHENEVER AN ABSOLUTE RULE TAKES EFFECT, A GREEN LIGHT FLASHES AT THE TOP RIGHT CORNER OF THE SCREEN.
3. APP CREATOR AILEEN IS ALLOWED TO FELLATE A HUMAN PENIS.
4. APP CREATOR AILEEN IS ALWAYS VISIBLY SHOWN ON THE APP "ABSOLUTE RULES".
5. APP CREATOR AILEEN IS ABLE TO TALK LIKE A HUMAN BEING THAT IS SIMILAR TO APP USER ROBERT LAURENT.
6. HUMANS EXPERIENCE NO SHAME RELATED TO THEIR STATE OF DRESS WHEN THEY ARE IN OR NEAR WATER.
7. APP CREATOR AILEEN HAS A BODY THAT RESEMBLES A FEMALE HUMAN ADULT OF 25 YEARS AND FUNCTIONS AS SUCH, BUT IT IS INFERTILE, HAS A PERFECT METABOLISM, HEIGHTENED SENSE OF SMELL AND A VERY HIGH LIBIDO.

Rob immediately he feels a wave of guilt wash over him. He just made Aileen infertile. Without her knowing about it beforehand.
Not even mentioning that he'd also locked the age of her body for all eternity and given her a terrifyingly vaguely described "very high libido".

He looks up and is about to apologize to Aileen for his clunky wording, but when he locks eyes with Aileen he's surprised to find her grinning ear to ear.
"Hell yeah dude! That's that good stuff! Looks like our session earlier left an impression, huh?" she cheekily says, wiggling her eyebrows in a comical way.

Rob immediately falls back into his usual stuttering response, the confidence he'd gathered earlier completely dissapated. "I- I didn't mean to... to... I'm sorry. I just wrote that your body would.. would be as human as you want it to be, or something. I thought I could give you the choice, I... Aileen I'm so sorry."

Aileen chuckles and puts her hands on his, covering the phone. She locks eyes once more and says: "Hey, it's all good. If you wrote that my body is how I want it to be, that has happened. It's how I work. Besides, the rule really did leave out all the worst parts of being human, didn't it? No periods, a perfect metabolism, amazing smell to appreciate good cooking and best of all..." She wiggles her eyebrows again. "a good bit of horniness to make use of all that dick sucking I ought to be doing."

Rob sits back with his jaws agape. "I-... You're not distraught about suddenly becoming infertile with **** in the matter?"
Aileen tilts her head. "Well, I did have a say in the matter. I told you to confirm the rule as you wrote it and you wrote it in a way that gave my subconcious control over the change. Also, I literally plopped into existence a few hours ago in a dark, somewhat dusty closet. I only just got my own bearings on what it means to be alive. I had no intention of taking care of any mini-me's anytime soon anyways, thankyouverymuch."

That gets an involuntary snorting laugh out of Rob and he shakes off his blanket stare. "Well that certainly puts it into perspective I guess. Still... I feel weird about deciding the fate of your body just like that."
Aileen nods in understanding. "I get that, but you have to become okay with the fact that these rules, purely based on how they function, will always give you power over others. Always." She pauses for just a second and adds. "You really did nothing I didn't want, Rob. I am as much that App in your hands as I am your roommate. Your roommate that is suddenly extremely hungry. You got any of that pasta left?"
Rob laughs, finally getting over his shock. He pushes the pot of pasta and the sauce towards Aileen.
"Absolutely, I did make enough for two after all." After watching her filling her plate, he adds with a grin: "Welcome to being human, roomie. Enjoy!"

She sticks her tongue out at him as she's adding cheese to her plate. "Oh wait so you're saying there's more to it than having a dick tickle your throat on your first day on earth?"
They both burst out laughing.
"Not much more, I reckon." Rob adds with a chuckle.

While Aileen chows down on her pasta with the ferocity of someone who's never eaten before, Rob lets his thoughts wander a bit.

Aileen was right, the rules will always be influencing someone. No matter what rule he writes, he'll be imposing his will onto the literal universe.
He still takes this event as a warning. Aileen might've been okay with the change, purely because she's also the app itself in some weird way, plus she seems to like giving Rob more power. It just might not always be this way. With this App, with Aileen, it is terrifyingly easy to change a person's reality by nothing more than the push of a button. Rob feels a chill run down his spine.
He's had the app for less than a day and he's already created a whole new person and changed the collective behaviour of most humans around water.
It's a hard thing for Rob to wrap his head around, but he agrees that he'll have to become okay with enforcing his will onto reality. At least in some capacity.
If he really plans on using the App for good, he'll change many, many more things about the current reality.

Small steps.
The first thing to do is to make sure Aileen is okay. Not just with her newly humanized body, but also with her becoming his actual roommate. That means getting a space ready for her to stay, as well as making sure she'll have all necessities like toiletries and clothing.
Then, he'll have another go at those severity classes for the rules.

"A penny for your thoughts, roomie?" Rob felt Aileen's foot gently tap his shin.
He sighs with a smile. "I'll have to get used to being caught daydreaming now, apparently."
"Daydreaming you say? Is it about me?" She cheekily asks.

He laughs. "In part. It's a lot to take in, this whole perspective change about magic being real and becoming able to change reality with an app." He stands up and starts to gather up the dirty dishes. "...but no, I was thinking about where you can sleep and if I have a spare toothbrush for you." It's his turn to wink at her.

Aileen grins as she carries the now empty pasta pot to the sink. "That's a good point actually. Man, being human is a lot more than good food and horniness, huh?"
Rob laughs heartily and starts loading the dishwasher. "Well those are the two most important things, but you do need a place to sleep, so --whoa!" He's startled by Aileen hugging him from behind.

She mumbles something into his back.
"What was that?" he asks, tensed up from feeling her body pressed up against his.