Having only recently escaped from just such a purse prison, you're in no rush to return to another. Instead, you leap down into her lap, not pausing before grabbing hold of the thick fabric of the dress to pull your quarter-inch tall self further up this mountain teen.
She obligingly sits still as you scale her, sticking where possible to her flank for the best of two options - hopefully not in her direct line of sight, yet still possible to see for yourself what's in front of her.
The girl is still focussed on her phone, and you've reached the upper limit of the dress's side - right below her armpit - when it suddenly begins blaring a pop song.
"Sorry," she says, rising with a swift movement and grabbing her bag, "but I've got to take this."
The giant strides from the room, you shimmying across to her front to avoid being smothered beneath the flesh of her arm. Not too soon, as once she's standing in the cool air outside, her hand raises the phone to her face, forearm crushing tight to her side.
"Thanks for getting me out of there," she says. "Every second inside with that bitch is a nightmare."
Seems that she can't stand the birthday girl either! Does that monster just 'buy' her friends?
"No, I haven't forgotten. Just waiting for the best moment. We just had the meal, now they're dancing - do you guys want to get eaten or stomped on by accident?"
What? What is she on about?
With her free hand, the girl opens the mouth of her purse, holding the space with a spread finger and thumb to peer inside.
"Relax, little dudes. I'll get you into position, no problem. Trust me."
Wow. Looks like those shrunken corporate spies the birthday girl mentioned are real, and this teenager has a number of them in her bag! This changes everything!
You currently don't have your shrinking device, so these guys may be the best way to regain access to your full size. You could push forward to full view of this girl as she looks down, and she'll spot you. Hopefully she'll be inclined to help, but who knows what she'll think of an unknown tiny man?
You could always go down to the bag itself, meet your tiny compadres and get to know them there.
The birthday girl may reward you if she learns of this treachery - you could let this girl take you back inside, return to the other purse and then try to earn favour by selling out these spies!
Staying out of these politics altogether is an option, of course. You could ignore this new information and continue with the plan you originally had to survive.
And now you're outside - you could climb down from this female and go out into the great outdoors to continue your adventure...