This is why I never, and I mean NEVER offer to do anything for anyone, or offer any favours, and I will especially not offer regular help or favours.
I know (and don't care) that this makes me sound like a really selfish old curmudgeon, but I am like this (now) because of bad experiences (like the OP is suffering,) in the past.
Even 3 or 4 years ago, DH dropped it out (in front of a few people in the local pub) that he has I.T. skills, and a couple who live in our village (15 minutes walk from us,) asked if he could help with their 'computer problem' (for free of course!) 
After that one time of helping, he became their 24/7 I.T. support. It became so annoying, having to pop round - immediately obviously - to sort out their I.T. and computer issues, that DH started to get really weary of it all. They even wanted him to go around and set up SKYPE ffs! They would say 'we'll only keep you ten minutes' and he was often there for 2-3 hours!
In the end I texted HER and said 'sorry but DH is not doing any more I.T. favours, because so many people are asking him now, that it's taking up half of his free time.' (A couple of others were asking him too, but not as often.)
She messaged back and said 'Oh, I didn't realise we were that much bother...'
I never responded back, but she AND he never contacted us again. (Clearly they were pissed off and offended that DH was no longer giving them free I.T. support.)
I will help people in an emergency (eg, a neighbour of mine asked me if I could run her up to the doctors some months ago, as she had been given an appointment for half an hour's time, and her DH had the car for work.) I didn't mind that. But I refuse to be a regular help for anyone. Been stung and burnt too many times, and taken for a mug (like the OP.)
@endofmytether26 As many posters have said, you need to make yourself a lot less available.
Plus, has this woman not got any family or friends? Why does it have to be you all the time who is running around like an unpaid servant for her?!