Make excuses
You don't want them knowing how bad of a trainer you are, so you make something up. You suddenly remember the man dressed in black with a Red R on his shirt. That's it! You tell them that your Charmander was stolen by one of those men.
"You were robbed by… TEAM ROCKET?!?!?" One of the kid exclaims. Suddenly you're drowned in a sea of kids all begging to hear more about the kid who survived an encounter with the renowned Team Rocket. You find out that Team Rocket is a dangerous crime syndicate, that abuses Pokémon to gain more Pokémon, in order to do their evil deeds. The girl happens to be outside and walks in on the commotion. She's obviously upset, but you have no earthly clue why.
"You! I said to head to the Pokémon Center!" She shouts as she yanks you out of the school house. You try to defend yourself, but she's not listening. You question why she's so upset, and when you do, she suddenly calms down. "No reason." She says, blushing. Something's amiss. "Let's just head back to the Center…"
Your Options
Refuse to follow her unless she spills some info
Follow her.
Run away from her!