Give her breasts.

Hm... you weren't sure it was such a good idea to try and convert her gender completely. Human hormones were complicated and testicles were fairly central to the male endocrine system. But you could help her be more feminine.

"I THINK I KNOW WHAT YOU WANT."

"Mfh?!" she struggled, shaking her head violently back and forth, eyes wide.

You resume your thrusting, piercing deep into her bowels with your slimy appendage. "MMM!" she resists vehemently... at first. But it doesn't take long before her groans are coming regularly and she relaxes back into your rhythm, closing her eyes. "Mm... Mm... MMh... Mmmm!" She's a squealer, that's for sure. She doesn't seem so worried about her mother anymore. You've stopped pulling in and out, now you're just pushing rhythmically against her prostate: wiggling against the sweet spot that gets her hot. Her little cock is peeking out from her panties once again and it spasms as you massage her balls.

Now that she's relaxed again you start on your real task. You project two tentacles up to her chest, settling the tips on her nipples and suctioning them tight. She moans from the new stimulation but doesn't open her eyes. Slowly, carefully, you start to worm tiny hair-wide filaments into the pores of her nipple. She doesn't even notice at first but opens her eyes as the pleasure becomes itchy.

You are just barely squirming inside the ducts, you'll need to make a few adjustments before the inflation could begin. You're going to need some female breast tissue to replicate in Carissa. Slipping a tentacle out to the still-**** Gabrielle, you clasp over her nipple, suction on and...you are met with a fine trickle of milk. Based on your understanding of human biology, there's no way she would still be lactating unless... Well, well, well, Mrs. Pereira. Getting freaky with her husband.

Inserting a tentacle-filament you travel up a duct till you reach the glands, taking a small tissue sample. Gabrielle coos softly in her sleep as you retract the filament, already starting to replicate the sample.

Carissa is having a hard time focussing long enough to figure out what you're doing. Her cock has slipped free of her panties and is bobbing in time with your thrusts. You work the filaments deeper into her nipples, reaching the small, undeveloped glands within them. You inject a localized anesthetic and begin maturing the glands, injecting a hormone cocktail you synthesized from Gabrielle's breast along with the appropriate cells. While you're at it you inject a bit of slime to increase the elasticity of the tissue.

It takes a few minutes to get everything in place but now all you have to do is inflate the glands. Carissa now appears to have minimal, A-cup breasts and she seems to have figured out what was happening.

"MhH!?" you wiggled a little inside her breasts just to confirm her suspicions, "MMMM!"

With that, you begin pumping in slime. Feeling devious, you add a bit of pleasure-slime to "assist in proper nerve development". Basically, this girl was gonna cum from breast stimulation at least as often as genital stimulation. She moans and groans around the tentacle gag, increasing the intensity of her thrusts back on the tentacle in her ass as she leans into the nipple stimulation. This was probably new territory for her, considering how non-existent her breasts were before now.

Speaking of which, her breasts had swelled to a large B-cup as you continued to pump them full of pleasure-inducing slime. They stood out nicely on her chest, this might actually work like you wanted it to (you had just thought of this like, ten minutes ago). She watched them expand incredulously, looking back and forth between them and you, obviously not quite sure how to feel. You corrected that by sliding a tentacle up around her cock and beginning to stroke. She threw her head back and yelled into the gag, bucking against the stimulation.

You finished pumping up her breasts, they now rivaled her mothers at a large C... maybe just a bit more... there. Solid double D's. As you retracted your filaments from her breasts you left a seal in the ducts to prevent your goo from escaping till the adipose tissue filled in.

Carissa groaned and bucked against your triple stimulation of her cock, balls, and prostate. She deserved a reward for going along so nicely. Re-suctioning her nipples, you begin sucking on them in earnest while massaging the pliant globes with your other appendages. She orgasms almost instantly, you feel her balls contract.

"NOT YET."

You tighten your tentacle around them, sealing the cum inside, and she goes wild: humping the air and struggling to throw you off. You increase the pace of your thrusts in her ass, pumping her dick at superhuman speeds, all the while sucking and massaging her breasts. Her eyes roll up in her head and she has several dry orgasms before you let her have the release she deserves.

Abruptly retracting all of your tentacles from her, you let her slide to the floor where she arches into the air and her cock explodes all over her upper body... Hm. Not much there. Little squirts of cum land on newly added breasts, her beautiful open-mouthed face, and finally dribbles on her stomach, pooling in her belly-button. Quickly spent, she flops back on the floor, gasping for breath while relishing the aftershocks.

You could probably fix that cum production problem...