How to make girl's follow me in GTA ppsspp?

You are asking about girls to follow you. So I'm assuming that it's not about getting a girl inside your car. To have a girl following you, there are 2 methods.

First one is for hookers. First get a good looking car (a sports car or a sedan) and find a hooker at night (from 19:00 to 4:59) and approach her from your side (driver side). She will walk near your car and stand there briefly for a moment. After that she will proceed to walk towards the passenger door of your car. At this point, exit from your car before she opens the passenger door of your car. If done correctly she will follow you forever (until you or someone else attack her or she dies).
Now second method, I'm assuming you are playing GTA Vice city stories. So there are some girls (not hookers) in the game, they just follow people around for some weird reason. They usually follow a male pedestrian. So try to find a girl who is following some guy on the streets. They usually spawn in downtown area mostly during daytime (most precisely, the road between the police station and fire department that leads to ammunation). There is a girl with short blonde hair who wears a crop top, miniskirt and high heels. She's infamous to follow guys in the Downtown area. So, go to downtown during the day and find them (the guy and the girl following him). After you find them, kill the guy (make sure you don't hurt the girl following him or else she'll be hostile to you. Use your auto aim button to lock on him and then kill him using your fists. Don't use gun to kill him or it may scare her. Go for a neck snap for an instant kill) If done correctly, she will start following you around until she dies or you or someone else hurts her.
Remember, these NPCs are just followers and does not provide any services like bodyguards or anything. They will not even get inside your car and will you on foot.