Yes, the day at a spa is a GREAT idea.
Also, freezer meals.
But another thing which she would appreciate would be if you offer to do some ironing, or vacuuming and dusting or something for her.
My freind had twins a few years ago and she chose to bottle feed. Every time a visitor arrived, all they wanted to do was sit and feed one of the babies. She told me afterwards that I was the only person who walked into her house and offered to wash-up and iron while she sat and fed HER babies. Even her own mother only wanted to feed the babies.
So, yes, doing the domestic chores would be a good one to offer. Maybe you could make some kind of gift certificate saying that you will do the chores.
You mentioned that she is in hospital now - I hope she's doing ok