When did she usually shower, what time of day? Did she usually take a bath instead of a shower? Would she prefer a modified bed bath instead of a shower? Perhaps she would take one if she felt like she was going somewhere after or getting ready for something. Maybe it’s the people showering her or the way they’re offering it that she doesn’t like. Sort through those questions and they may give you a way to get her in there. What’s her reason for not showering? Can she verbalize a reason?