OP, you sound like an awesome SIL.
I just want to thank you on behalf of all SIL's who have been treated like shit from their SILs, and have never received any reciprocity over the years. Thank you for being thoughtful and kind.
You can't go wrong with flowers. Maybe a gift card to a local food delivery service or grocery store, or her favorite restaurant (to use when she gets better, or to order from while sick at home).
Dean & Deluca often has nice edible food gifts.
On the pricy end, Olive & Cocoa also has great savory food things.
I can't speak to experience, but there are a number of online Trail Mix websites - Jerry's Nut House, Nuts.com, that do gift orders.