Replacing baseboards in my house and I come across
a rounded corner in the bathroom.
do you have just this one corner issue to address in the whole house ??
in my world, the horizontal baseboards goes on after all the
vertical case work as been done. then fine-tune the base
to meet the vertical trim. (but, that is just me).
when I have had to use wood base molding in a rounded corner,
I made myself a soft cushion of folded up drop cloths and broke out
my favorite can of Bondo to artfully finesse the molding to match
the round corner. (IF you wanted to go that route).
if you are not in a hurry, you could fabricate a small (2x2') duplicate
of your corner and practice making the molding fit (visually).
then, you could sit at the kitchen table or your shop work bench
to do the practicing.
others more experienced than me may have a better solution.
keep us in the loop with photos when you get started and the finished project.