Shocking

I can't believe the phone conversation I just had. A flatmate of mine who moved out back in December, and who I haven't talked to since (intentionally) just called me, wondering if I'd like to do something, go out for some food or drinks. I didn't really feel like it, but I also didn't really feel like making excuses, so I tried to be kind of non-committal without being rude. Then she said "oh, but, uh, there's one thing, uh, I don't have any money with me." She's managed to lock herself out of her sister's flat, where she's staying, and called me to go for dinner so I could pay for her. Now, if we'd been in touch, and were any sort of friends, that would be one thing, but she's calling out of the blue, asking for me to buy her dinner? I mean, ok, so she's locked out of her place, but I mean, that happened to her at least 3 times while she was living here, she needs to learn to stop misplacing her keys. I'm feeling a bit annoyed right now, because I feel so guilty for pulling the whole "I've been out all day, I just want to stay home and relax" thing, but what else am I supposed to do? I wish I'd never given her my number.