I'm 36 and I come out with odd words and phrases or use words/ phrases in a different context to when I'm meant to. But I often forget words and do the describing of imagery because I can't find the correct word. I have anxiety, adhd, asd and cfs/m.e and fibromyalgia; my poor brain is in a constant state of overwhelm and overworkedness.
Sometimes me and my family use weird words or descriptions etc because we ARE weird and a bit different. It runs down through several generations.
But there's also childish things about my mum, particularly, which have caused her to be picked on over the years and which even I have been embarrassed of, myself. Only a few times have I ever mentioned anything to my mum. The rest of the time I try and ignore it.
If she spoke to me constantly like yours does then I do think I'd be cross - specially if she seemed to use it as a means of not having meaningful conversation.
A good friend of mine who I've recently lost touch with, doesn't discuss his emotions properly and avoids meaningful conversations - with a mixture of going silent or using funny words and phrases. He also uses a funny voice. I've always found it endearing, but I've always been sad that he can't express his real feelings. There have been times he's really wanted to but has clammed up and returned to the strange phrases and voice.
I don't know what's going on with your mother. It would certainly piss me off at the level she's doing it at. But it sounds like there's something else going on with her. Like she's hiding something or avoiding deep communication.
I had to look up neologism. But it makes sense now. Neologism can be a bit of fun but at the level your mum does it, I don't see it being fun, but making people wince after a while.
YANBU, but at the same time she's every right to be that way. No advice I'm afraid. Perhaps just do it back but with rude words - "mother, do you fancy a defecation of coffee", or something 😂 don't let her read A Clockwork Orange whatever you do.