I'm no theologian.
But I think the phrase is "charity begins at home but does'nt end there", realistically you don't need to refer to the Bible in order to solve this problem.
If you've lent her money before did you get it back without a problem?
If so then the next thing you need to ascertain is how much she wants to borrow, if it's alot of money (say over �100) and you have'nt got it then personally I'd say no. I have a rule of never lending more than �50 to anyone other than family I would'nt dream of asking a friend for more than that. I'd be appalled if I asked for �50.
If you're concerned about her wants and needs and don't want to risk offending then offer her half of what she wants.