Make her start laying eggs

Curious to see if the Ruby can alter more than just her appearance and feeling rather mischievous, you wait until Erica starts blowing on her coffee, then focus on her again and say, "Starting now, you will lay at least one egg every hour from sunrise to sunset. The experience of egg laying will not be painful for you, instead feeling entirely pleasurable."

You don't notice any immediate changes come over Erica. Still, the hair color change wasn't instantaneous either, so you resolve to be at least a little bit patient. Erica takes a sip of her coffee, then looks up and asks you, "So, what made you decide to come over? Other than boredom, of course."

"Really, that's it," you say, watching your friend intently, "I just figured the two of us could hang here for a bit, maybe watch a movie or play video games."

"Yeah, that sounds like fun," she says, and you notice her squirm a bit in her chair, "I'm totally down for a couple rounds of Mortal Kombat if you're interested. Er, but first I need to go to the bathroom real fast."

Erica stands up and starts making her way to the bathroom, but stumbles about halfway to the hall. She stops and places a hand over her abdomen while leaning on the counter with her other arm.

"Are you okay?" you ask, standing up and walking over to her.

"Yeah, I'm fine," she tells you, though she's breathing heavily and still clutching her abdomen.

"You think you can make it?" you ask her.

"Mmmhmm," Erica says with a nod, pushing herself off the counter and walking forward. She only takes a few steps before she lets out a whine and puts her hands on her knees, "No, shit, no I can't. I'm gonna piss my pants!"

You get around in front of her as she spreads her legs and squats down about halfway to the ground. Bemused, you ask her, "Wait, seriously? Is that why you're squatting like that?"

"It... feels right... and it helps with the, um... the..." she pants, her face going red, "Shit, it's not... it's not peeeeee."

The last syllable came out as another high-pitched whine. You see a wet spot start to appear on the front of Erica's sweats.

"What is it?" you ask, eyes transfixed on her crotch.

"I don't know," Erica gasps, "But whatever it is, i-it's coming! And stop staring at me!"

"I'm sorry!" you say, "This is just so-"

You're interrupted by Erica letting out a loud moan and shuddering, dropping lower into a full squat.

"Erica!"

"I'm fine!" Erica moans, her breathing quickening, "I fine, it's just... oh, oh God!"

Erica presses her lips together and lets out a sound somewhere between a whine and a grunt. In an instant the front of her sweatpants is absolutely drenched, and shortly thereafter a large bulge pushes outwards from her crotch. Erica lets out a long sigh of relief and catches her breath, still squatting in place.

"Are you alright?" you ask her.

"Y-yeah," she stammers, shakily staring to push herself up, "Horribly embarrassed, but, um... alright."

She suddenly freezes, still partway bent over, her eyes widening in shock. She looks down at her pants, noticing the bulge in them for the first time, "What the fuck is that...?"

Forgetting any sense of decency, Erica stands upright and sticks her hand down the front of her pants as you watch. She fumbles around for a bit, then shakily pulls out the object in question. It looks like a chicken egg, only noticeably larger, and covered in a slime that you assume is Erica's pussy juice.

"What the fuck is this...?" she repeats, staring at it.

"It looks like an egg," you point out.

"No shit it does!" Erica yells, "Why did I just lay an egg?"

"How should I know?" you shout, in an attempt to avoid laughing.

Erica sets the egg on the counter and steps back, "Okay, this is too freaky. I need to get cleaned up. Just... I don't know, google this on your phone or something."

She rushes off, her face red as a beet. You wait until she's gone, then chuckle giddily to yourself. This amulet was amazing! You're pretty sure that if it could do this, it could do anything you wanted! And in an hour, you'd get to see the whole show again.

Except from the bathroom, you can hear a muffled whine through the door. It seems like the Ruby took the 'at least one an hour' part of your statement literally, since it hadn't even been a full five minutes since her last egg and she might very well be laying another from the sound of things. This was going to be a fun day, at least for you.