I too have a neighbor like that, and worse yet, we work together too. She will come over and ask to borrow butter, onions and even bleach. I don't mind helping out once in awhile either, but I have asked her twice for something and neither time did she have it. And to make matters even worse I needed a ride home from work two different times and when I asked she just said that she had something else to do, or she wasn't coming home, yet, when I got home her car was there already. She said to me one day when she was having car problems that she might need to get up early and go in to work when I do b/c her car wouldn't start- so i told her my hubby had a meeting the next morning and that I was going in extra early and I didn't think she would want to go that early.
I have pretty much learned not to ask anybody for anything, and try to stick to my guns and say no when people are always asking me for stuff.
See, getting me started on something that drives me crazy...LOL!