How often should I suggest Mom shower? I’ve been doing every three days. Is that enough?

I've really got nothing to add other than to point out the daily bath/shower is a fairly modern concept and not really necessary for health, just societal expectations. Where I live in AL they pay extra for more than one assisted shower a week, and in the nursing home they get two.

If you think so, and she thinks so, and assuming basic hygiene is maintained with washes in between, then yes it is.