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The seat cushion I have takes the pressure off my tailbone.
This is the one I have: https://www.amazon.com/Cushion-Orthopedic-Sciatica-Tailbone-Support/dp/B01MZ8IVP4/ref=sr_1_3?ie=UTF8&qid=1527515917&sr=8-3&keywords=ziraki+seat
Have had it for almost a year now and it is still in great shape (my fiancé bought a similar but cheaper one and it pancakes when he sits on it).
Sleeping wise: I bought a super firm bed mattress (like, it felt like a table when I first got it) and sleep only on my back with a thin pyramid-shaped pillow beneath my lower back for added support. This has all significantly helped.
Definitely keep her moving! You can also ask about air mattresses. You didn't mention where the wound was but Amazon has some cushions with a cut out for the tailbone which was a lifesaver back when my grandma was well enough to sit up on her own. I'm not sure what brand we got but it looked just like this: https://www.amazon.com/Cushion-Orthopedic-Sciatica-Tailbone-Support/dp/B01MZ8IVP4/ref=sr_1_21_sspa?crid=ZUYU023IWKJP&dchild=1&keywords=pillow+with+tailbone+cutout&qid=1595910602&sprefix=cut+out+tailbone%2Caps%2C537&sr=8-21-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEyMDBBWEQ2WVk5WUMyJmVuY3J5cHRlZElkPUEwODEzNDE3M0lYQU83R0o0RUpFQyZlbmNyeXB0ZWRBZElkPUEwNTcxNzQ3MjhFREhGUjVUMEdJJndpZGdldE5hbWU9c3BfbXRmJmFjdGlvbj1jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ==
Or you could try one of these that keeps the person shifting their weight when they sit. They had this for my grandma last time she was at the hospital (again you don't have to buy this brand this is just an example): https://www.amazon.com/Inflatable-Construction-Durabilityd-Prolonged-Approved/dp/B00XBK33X2/ref=sr_1_5?crid=YAGLHWMNIKRX&dchild=1&keywords=air+cushion+for+pressure+sores&qid=1595910835&sprefix=air+cushion+for+pressur%2Caps%2C310&sr=8-5
Protein helps tremendously, I can't stress it enough. Sneak in some protein bars or drinks whenever possible. Lastly ask about DuoDerm (Hydrocolloid Dressing). You can buy it on Amazon and it's basically a huge bandaid for deep wounds. It essentially makes the skin thing there's already a scab on top so they start healing faster. They only reason I say ask first is I'm not sure how it would react with whatever ointment they gave you, but again it's on amazon so anyone can by it. The skincare community uses it to fix pimples in 24 hrs, lol. There's also medical grade honey for wounds but I don't know where to purchase that.
Oh and use a flat sheet instead of a fitted sheet when she goes to bed. Fitted sheets don't move with the person and create friction on the wound. Just take a regular sheet and drape it over the bed in place of the fitted one.
Hope some of this helps!