I have had a similar surgery and I would have appreciated if someone had made and froze a few meals for me I did do some before I went into hosp but if yu were to turn up with a few when she comes out I'm sure she will appreciate it.
You could also buy her a book instead of magazines as she will be immobile for quite a while and books obviousley last longer.
AFAIK unicorn if you have a hysterectomy you have to have at least six weeks off work and not drive for that long either. I think some practical offers of help would probably go down well - along the lines of "I'll do x for you" or "I'll come on x day" rather than "ring me if you need me". Even though she's got someone coming to help it may be nice if she's got more offers - eg cutting the grass, cleaning windows, taking her to the hairdressers etc.
I couldn't do anything fo six weeks. your friend will also be unable to drive for six weeks so a couple of 'day trips' will be appreciated. You could take her to the park for a slow walk or for lunch or even just to your house as a change of scenery will be great. Nothing too energetic as I was always tired but loved getting out