R.L.
My 5 yo son went through a phase just like this when he was 4. I just told him that if he wanted to take a bath he needed to ask me, and if we didn't need to go anywhere I would usually let him. He would take about 3-4 baths and most of the time played for 20-30 min. I can't explain why he wanted that many baths but it only lasted for a few weeks...and then it was on to the next phase. But he is also my water baby who loves the water and is the most comfortable in it.
I would work on the communication factor of her letting you know when she wants a bath...that can be a building block to communication later on for bigger matters