Cats usually do things other than peeing inappropriately to get our attention. Galaxy is trying to tell you something, and that something is very difficult to find.
Make sure that you provide a litter box with a very low entry, in case she does have arthritis.
Years ago, when Monroe was still around, I made a litterbox out of a large storage box with high walls, because he would pee standing up. It's basically a "walk-in" box, and the cats love it.

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