To be blunt, she may be your mother and very dear are all mothers to us but she is one person whom it appears doesn't rate your compositional skills. However you have evidence that plenty others do so why worry about one person's opinion?
Allow one hundred people into an exhibition of say 10 great photographers' work and I'll guarantee that at least one of the hundred won't like some of the work on show and cite composition among a myriad of other reasons. Here's another guarantee. They won't all home in on the same work or even the same photographer
Value your mother for what you believe she is good at and accept that she may not be a "born photographic critic"