So its getting in the shower in the first place... when in there she can stay in a while and how good a job she actually does of washing sounds pretty 'standard for kids' really.. good somedays, crap others.
I hate showering, HATE it, once I am in I do a decent job of it (bearing in mind I also have a physical disability and sit on a stool in a walk in shower and still need help)...
Before all the physical issues though, I still hated it, but I also didn't really like feeling dirty or stinky either... and no way could I have put into words at 10 why I hated it.
In our house there wasn't really a clear cut time for a shower and so any shower was rushed (we were a 'bath once a week, shower when you want' family, it was the 80s...).
It was VERY cold, bathrooms really cold, most rooms generally cold. Heating rarely on and when it was the heat just went up to the top third of the room which served no one any good.
Mostly though I now realise it was sensory issues, I didn't know what sensory issues were as a ten year old though. I knew that I hated being cold, shivering, feeling my relatively warm, dry skin getting wet and the tingles that triggers, the sore cramping muscles from clenching up when cold, the cool breeze on wet cold body...
Then after the shower there was the crispy cat-hairy towels, and only one and it didn't wrap around me at all. A brisk scrub down with it and then dressed, usually whilst still damp with the awful feeling of clothing sticking to me.
Ugh ugh ugh. To shower now my house has to be tropical hot, I am in enough pain already without adding in more muscle spasms and soreness from getting cold.
So I would ask about sensory issues, does she hate the feeling of x or y, many people do!
Ask her what would make regular showering easier, fluffier towels, bigger towels, warmer room.
Not being stinky is really a non-negotiable, but there are alternatives to showering (believe me, I didn't shower for YEARS before we got the wet room in January)..
There are shower wet wipes you can warm the whole pack in the microwave and just wash one bit a time, covering up the rest whilst you do so.
There are shower foams you squirt on, rub in and towel off too and used regularly these are very effective.
What if she showered once a week, to do her whole body and hair, and then used these options the rest of the week?