Should I pay for my friend to go to the movies?

Kay, so we planned it out last week already. I'm a really generous person and I stopped being a push over a while ago to people who are always asking from me. You see, she's my best friend and I'M the one who invited her. My mother is paying for us but I don't like to ask from her because we aren't wealthy and she works hard (single mother) and I'm afraid she can't afford three people (her, me & friend) But I asked her if my friend can come (put in mind we planned this for a week now) and she said "Well, is she paying too?" and I don't like it if my friend pays because somehow I find it inconsiderate because I'm the one who invited her. My friend told me she would pay though but from knowing her....I know in her mind that she's thinking that I'm going to pay for her (because she doesn't like paying...) but she has two working parents and they have money so it wouldn't be so bad....anyways ...you think I should reconsider and tell my friend I'm not able to pay for her and that she should pay for herself?