I can't really see any sores as such, but if its the yellow marks is it the start of urine scald? Her hair looks a little yellowish too on the left-or is that a patch of normal coloured hair?
I think if is, she may have a bit of a smelly bum too.
If she was mine I would give her a tepid bum bath &dry her off thoroughly (gentle patting with a soft towel or low heat setting on a hairdryer (one of mine loves the blow dry!
)
Just smear a THIN layer of sudocream on the marks (not in her opening only around it).
This will act as a barrier against the urine &heal/soothe it at the same time.
If she is an older lady maybe check with the vet its not pain or arthritis related &which is making her want to stay in the same position longer &sitting in her urine
It could also be a urine infection/mild cystitis causing her to dribble/leak a little.
Discuss with your vet about painkillers tho as this may make her move around more ¬ sit in her urine.
If she's in pain she may loose her appetite so keep an eye on any weight fluctuations or reluctance to eat.
If it gets worse or changes significantly (colour,size or shape)definitely book a vets appointment.
Healing vibes. Xx