You offer to lick her pussy (with some help).

"Do you mind if I take those off," you say, "I saw how good Tia licked Amber's pussy earlier and I got a little jealous. I want to show how good I can be...but maybe also get some pointers. You down for that?"
"I'd be glad to help you," Tia says, "It is up to her though."
"I...I always wanted you to lick my pussy," Trish says, "I was going to let you do it after the Concert, but you changed plans."
"No time like the present then."

You clear the distance between you two, Tia following shortly behind you. You get down on your knees in front of the blond teen and reach for her panties.

She nods in acceptance and you pull them down, Amber helping her stay balanced while she steps out of them.

Her pussy is quite lovely, just a small tuft of hair sitting above her pink lips. She's a little wet, making you think that she has been masturbating today.

"I like a nice, clean pussy," you say, "Don't you agree, Tia?"
"I do," she replies, getting down next to you and eyeing the girl's flower, "So pink and lovely."
"It just really needs to be licked now..."

You start to lick her pussy, focusing on the outside of it first. Trish looks down at you as you do and smiles. Amber is cuddled up next to her and whispering in her ear.

After a couple of minutes, you move to the inside of her pussy, giving them some love too. You slow down a bit though...

"How am I doing so far? Any pointers," you say, looking at Tia.
"She seems to like it. There's a trick I can show you...assuming that she's okay with me eating her pussy."

You don't mention catching her and your Sister in a sapphic love-fest (thus setting up your arrangement with her). Amber whispers in Trish's ear again and the girl nods.

You turn her a bit to the side, presenting her pussy to Tia.

"I'll show you how to give her a quick, small orgasm. You repeat after me and then we can give her the big one."