hmmmm not an easy one and every situation is different.
If it was me I would price the job up with something I’d be happy with whilst giving enough discount to make you feel good about yourself but also say to her that you'll happily do it for peanuts but it will have to fit into your schedule when you have a few hours here and there so may take 3/4/5 weeks to complete and you may even chuck in some surplus materials. But you do have to like the person as your in business and it is stopping you from earning elsewhere.
But you do have to weigh it up; I’ve been down this road before. One of the guys that worked for me was a church goer (but not the preaching type, he was as bad as you and me!) A lady from his church needed the exterior of her house painting; it was in a really bad state and had a hell of a lot of woodwork that needed sorting out. I agreed to help him and we'd do it on the cheap as this woman didn't have much money. My normal price for doing something like this would be around 8k but we agreed that we would do it for a day rate of £80 each! And it would take around 3 weeks so a rough price of 2.4K+ (that's less than a 3rd of the normal price). I wasn't really doing it for her; I was doing it for my mate as he really wanted to help her. On top of this she got the scaffold towers for nothing and we used some surplus material for free, in the end it took 4 and half weeks because it was so bad, so the total bill was going to be 3.6k. My mate didn't want to charge her that but I was adamant that that was a more than bargain price. The thing is, she lived in a house that when she bought it 30 years ago it was in an unpopular area and might have cost her around £40k but on today’s market would fetch around £450k+ and we had just increased its value by around £15K on the work we just did! Now who's the mug! She clearly couldn't afford the upkeep on the property as I doubt it had been painted since she bought it but is that really my fault? She’s sitting on a rather large nest egg, the fact she was unwilling to remortgage or downsize should not play on our good will, I certainly don't have that much equity in my property. And to top it all of her husband was the caretaker for the church! (although he was crap) In the end she was charged £3.6k but I later found out that my mate gave her back a considerable sum which made me feel like a sack of ****, I wish I never got involved.