This week I landed myself in a walking boot for the second time in two years. We still have snow patches on the ground here, and on Monday it snowed, rained, freezing rained, and ice pelleted all in one day.
IME, the "My Recovers" walking boot weather covers do a good job of keeping the boot dry as long as you don't go slogging through puddles - they are open at the bottom so you still have the benefit of the non-slip traction of the boot bottom.
https://www.myrecovers.com/Walking-Boot-Covers-Outdoor-Weather-Covers-s/1852.htm
I bought mine via
Amazon.
A few notes:
- they get HOT and since the fabric is waterproof there is no way for them to breathe the perspiration out [not that the boot itself does any kind of job of that either - in warm weather by the end of each day my sock inside was soaking wet - so just magnify the limited breathability of the boot with no cover by no breathability and you get the idea], so take it off if it isn't needed;
- bring extra liner socks. I just bought two more [via Amazon] because this time round I didn't want to be washing a sock each night for 6 weeks. BTDT. So I now have three socks and can rotate them and only need to wash 'em all every 3 nights

But also, when you have to wear the liner cover or when going around in the wet, a change of liner sock may be needed mid day.
She may also need an "Evenup shoe leveler" for her other leg. Two years ago I didn't use one because I had a pair of shoes whose heel was thick enough, but those shoes really made my good foot unhappy [I had stopped wearing the shoes a while before for that reason]. So this time round I bought the Evenup and used it for the first time today with one of my favourite shoes. Massive difference. I HIGHLY recommend. I bought mine via Amazon with next day delivery.
http://www.evenupcorp.com/
Good luck !
SW