Go to a gallery and see what works most of what you show is hung way too high , don’t stagger pieces on a straight wall for sure and try to hang ones with similar subject or color in the same space.

I'm sure she loves her art and even if you get her to agree to reduce by one or two there still needs to be a plan - groupings are best to calm the eye and also highlight pieces and ensure pieces have a similar feel either with frames, matting, colors, etc. I would remove the piece the by window and next to the large piece in dining room and add to the wall with the two yellow/blue pieces, as they work together and would be a nice focal/neat arrangement. Place the large piece that is over the buffet to over the couch and keep that wall simple and calm. Use the wall in the dining room for the collage and don't line up horizontally as much...see below. Keep in mind height when hanging...better too low than too high. Also suggest she edit the accessories on the buffet, so it feels less busy. There are lots of articles to help with eye pleasing arrangements and play around with configurations on the floor first.