Give one a genuine compliment and you can maybe say something like….
…”Hey I am making new friends and wanted to give you my number just in case you [want to hang out/ ever need a ride/ miss a class and want the notes/ want to go shopping together].”
What if she asks: Why are you making new friends? Are you new? What happened to your old friends?
You can say, “I’m growing and realized that it would be good to branch out and find friends that are committed to Yiddishkeit and like going to shiurim in the area.” — or something that feels more natural for you to say.