What Do I Do please help

Okay So my sister in-law wants to get her lashes done and so do I , she just got paid Friday she wants me to pay for hers and my (15$) deposit appointment for both me and her ( lashes are 50$), she told me she’ll pay me back but has a history of paying people back when she feels like it or sometimes she won’t pay them back at all ( I know it’s only 15$ ) but when money’s borrowed from her she wants it back ASAP , She’s mad because I didn’t make the appointment I told her I didn’t have money but I’ll help her make the appointment for her so she’ will for sure have an appointment she said this “ wow my brother can’t even give you 15$ for the appointment how sad “ and “I’ll just let you know Wednesday I guess “ n gave me a really dirty look he of course is ganna give me the money .. I’m the type of person who don’t like confrontation she likes to take advantage of my kindness .my husband got mad and said if she has money to get her hair done an her eyebrows done she can pay for her appointment do not let yourself, am I wrong in this situation I feel bad

Sorry if I’m all over the place . I hope this makes sense