Now that summer is here my kitten (female) likes to spend a lot of time in the bathroom…

Cats and kittens will naturally seek out cool spots if they are too warm. Often they will lay on hard cool surfaces and many spend their time on the floor rather than up high where it is warmer. The best thing to do is prevent your cat from being exposed to high temperatures. Use fans or air-conditioning if indicated. A bath is not necessary and I usually do not recommend unless there is an underlying reason (like your cat rolled in an oil puddle). A bath would only give your cat a very short term cooling effect and tends to be stressful for many cats.