The thorny question of money etiquette

I am in a bit of a tricky situation and I hope that someone can help sort it out.  It's a long story, but here goes, with some background explanation:

I currently live in Somerset with my in-laws.  We are in a rural area and I don't drive, so I wasn't able to find a job locally when I first arrived in the UK.  I finally decided that the best thing to do would be to look for work in Bournemouth (I did my teacher training there so I know it well and there is lots of work there for EFL teachers) and I soon got a job there.  However, it is too far to commute daily so I ended up having to rent a room there during the week and go home at weekends.  I did this for about six months, but left the place I was staying before Christmas because I wouldn't be back at work for at least six weeks, and DH and I were planning our move to Dorchester (whence an easy commute to Bournemouth) and I hoped we'd have our own place before I returned to work.  However, my school contacted me in mid-January to say they needed me for the week of the 25th.  We weren't scheduled to move to Dorchester until the 1st of February.  So I had to find a place to stay in Bournemouth for that week.  I contacted the woman I'd been staying with before, but she had another tenant.  I answered several ads on Gumtree but they fell through.  I asked for help from one of my work colleagues, who said he would ask around the staff room to see if anyone had a room to spare, but then silence.  I was about to book a hotel when I got an e-mail from the colleague saying that another teacher had a room I could stay in.  I called her and we arranged the time I would arrive and discussed a few other things.  We never mentioned how much she would charge, but I had always fully expected to pay for the room.  However, when I arrived she still didn't mention it, and we were so busy chatting about other things (we have always gotten along well and been friendly and chatty at work) that I wasn't sure how to bring the subject up.  Plus, she acted like I was a guest, and I was worried that if she saw me as such, then I might offend her by offering her money.  But on the other hand, I don't want her thinking that I was expecting to get everything for free and ending up resenting me because I didn't offer to pay.  I really like this woman and I don't want money resentment coming between us.  And I mean, she gave me a place to stay, I ate dinner every night with her and her daughter, and she drove me to and from work every day.  I owe her something for her generosity, but I am really unsure of how to handle this.  Do I offer her money?  If so, how do I bring up the subject gracefully?  Maybe I should just get her a gift?  She just had to pay £200 to get her car up to scratch for its MOT, so I really think money would be better than a gift, but I am hopelessly awkward with delicate subjects and I really don't want to offend her.  Help?   

Have you asked the colleague who put your two together in the 1st place what she might be expecting?

I would just put some money in an envelope at the end of the week and give it to her, saying this is for this week's rent, let me know if it's not enough.  About £100 would be a reasonable amount as it includes meals & hot water etc.  She probably is expecting you to offer something rather than having to ask you.

Yeah, I'd just give her money rather than wait to have her ask or bring it up... A learning lesson from me- when I was staying with my friend for a month, she ended up awkwardly asking me for money- because I was  actually debating the same things you were and didn't know how to bring it up or what to say
I felt like a right prat in the end

I agree. Just give her an envelope. The worst that could happen is that she isn't expecting payment, in which case you'll be slightly embarrassed. But that's far better than appearing rude by not giving her anything if she is expecting it.

I agree to give her an amount that you feel comfortable with.  But approach her and tell her how much you've appreciated her generosity and that it's to offset any expenses she might have incurred.  Since the subject of rent wasn't brought up, I'd say it wasn't expected and wouldn't advise saying the money is for rent.