Thanks, all. I've confirmed plans with Nephew's wife and I'm stopping by Nation's for the pies (yum!) on my way up there.
I know I don't owe my SIL anything, in fact, I should be avoiding her like the plague. She made my relationship with my PIL's very difficult when I was dating, engaged, and first married to DH. A lot of the bad behavior could be directly attributed to her drug use, which my DH refused to put up with, so we were incommunicado for several years.
SIL has never been and will never set foot in our house. We are not willing to trust her near our stuff, on the chance that she will steal or will tell her druggie friends what we have to steal.
She supposedly is now drug-free (except for the methadone treatment), so DH and I took the chance that there could be a family relationship. DH is working constantly, so a bit of the burden has fallen on me. I know that if DH were with me on visits, she would not display these behaviors, at least not the more egregious ones. I am limiting these visits to once/month or less in the future, if only so I won't be asked to change the dressing again. There are things one shouldn't see and my SIL's bottom is one of them.