I’m trying to do something to make a girl feel better about herself

Maybe show concern.. ask her if she's gained aby weight lately.. but be nice about it.. like you want to help.. that uiu just don't want her to get fat like her mom did.

Tell her she looks pretty and hang out with her <3

Good compliments

Updated: If it's a usual case, it should work the way it works for all.

Give her compliments on the way she looks and her personality. Be positive and encouraging

Yes but I'm not rich enough to be a sugar daddy

Take her to do an activity she's good at and enjoys

A girl you or a girl someone else?

Show her how loved she is.

Go on a walk.