I'm in the reverse situation in that I moved in with my Mum to help her! But I guess certain things remain the same. I think the most important thing is to have some ground rules around who does what. If you haven't already, I would suggest sitting down with her and asking what would be helpful and what would NOT be too! And also making clear what you can and cannot do. That way, hopefully, you can help each other without treading on toes too often!
Also, it is really important to have some time apart. Maybe join a craft/hobby group, a gym, library, or find a local community coffee morning - anything that means you have some time apart doing things with other people.
Do you know what caused the issue that ended up making you cry? It would be worth thinking about it, trying to see what upset each of you, so you can both try to avoid it in future.
It is possible that your daughter may be feeling guilty in some way that she has had to accept help - she may feel that she is grown up and should have been able to cope on her own. People in this situation are often extra-sensitive, so try not to take things too personally. Wishing you both a happier rest of the year. x Dorothy