Oh yes, this EXACT thing just happened to my horse -- she had stitches from a surgery and had to be on stall rest for 2 weeks as well, NO moving her out of the stall at all! And there are a few tricks I used to keep her from going insane:
1. Get a milk/water gallon jug and poke some pellet-sized holes in the bottom and leave the top cap off. Fill with a handful of pelleted treats - if your horse moves the jug the right way, she'll get a tasty treat! Hang from the ceiling or the wall -- I had 2 of these in Sandie's stall and one also had a handful of sweet grain which would fall out more easily and kept her attention.
2. Teach your horse tricks
Now this isn't for all people, but for those who wish to teach tricks, it definitely keeps the mind occupied. I taught Sandie how to "shake hands" during her stall rest, by using tic tacs as treats, I just tapped her leg and then picked it up and said "Shake" and rewarded her. Now all I have to do is reach my hand out and say "Shake" and she does it! HOWEVER, as with any trick you also can't give the horse a treat whenever they do the trick, which they will try all the time without you asking first just to get one! Only give the treat when YOU asked for the trick...otherwise someone could walk by and get swiped by your horse's hoof!!
(Sandie's still learning not to "shake hands" unless I ask her now!!)
3. I know you said your horse isn't a fan of salt blocks, but have you ever tried the flavored kind? Sandie LOVES peppermint flavored and candy apple flavored salt blocks!
Other than those ideas, I'd say just be sure to visit every day and groom her, talk to her, just hang out with her in the stall. All of the above helped Sandie not to go stir crazy -- but don't get me wrong, even so, the first day out of her stall she went CRAZY (DO NOT ride that first day lol)
Hope everything turns out okay for you and your mare!