Girl owes me money, but avoids me

This girl i used to know in primary school goes on my train, and a month or so ago she asked me for my debit card because she lost her zip card. I gave it to her, because I just assumed she would pay me back. She didn’t scan it properly and it charged me £10 (it was 3 stops). I asked a mutual friend between us to mention it to her, because I don’t have her number, and I don’t see her in school. When i do see her, she’s always with this massive group of friends, and it just feels awkward to ask her in front of them. I saw her on the street last week, and started walking towards her to ask for the money back, and she’s obviously avoiding me because she always walks away even if we make eye contact etc. it’s been a while now and i’m not sure what to do, because she won’t even give me a chance to talk to her. Out mutual friend is covering for her i think, because she said something along the lines of : she’s fragile right now. Like, just give me the tenner 😭😭😭 i know it’s only £10, but still 😭