Hi Shadow,
I'm so very sorry about
your Mother-in-law. My deepest sympathies to you and your family members.
I am, however, glad to know that you are doing the foot soaks! Stress like what you are going through can really reek havoc on someone who has these infections! So do your very best to get the rest you need, eat well, drink plenty of water (aim for 64 ounces a day) and keep up with the detoxing. These things will help make this time a little less miserable with your body.
AS far as footwear, get a shoe that has good support all around the foot, and has a good sole on it. I like boots, but there are some pretty good tennis shoes that will give your foot good support.
Do you have an old fashioned shoe stores any where near you? If so I would suggest that you go there and get fitted and tell them you need a really good shoe that has really good support. Then let them bring you the shoes to fit to you. Once you know what shoe you need/want, go find somewhere less expensive to buy it!