I am so sorry for the stress you are under. Had I received that letter, the tears would have started (the last straw tears!). I do not know your situation as far as friends, church, or other groups... but sometimes (cub or boy) scouts are looking for volunteer projects, church youth groups, or just nice people. Give them a call about your yard. I am a middle-aged woman who loves to mow... I guess it's relaxing.
Anyway, if you have people who always say "if there's anything I can do", please let them know. I know sometimes you just want them to see what needs to be done and do it. But, often they are afraid of doing something like your lawn without being asked because they don't want it to look like they think you can't handle it. I would do anything for a friend but didn't know to just go ahead and do it until I was in the same situation myself. Now I know next time to act without being asked.
Things will be better one day. Hang in there.