Honey08
Waffled a lot!
Yes do get something in writing, but really she is doing you a great deal - she could rent the stables out and hire herself a groom with the proceeds to look after her horse, who probably won't be much trouble... She probably thinks it would be a quieter less stressful route to have one nice person around (heck sounds like she has had her share of stress!). Go and have a really good chat with her, suss out if you think you will get on etc..