I first brought my gal swimming at around 3 month plus. Just so she can get used to it rather then fear the water. Bring a float and sunblock on top of the other normal things you bring when you bring her out.
Remember to keep her warm after you get out of the pool. I usually give my galher milk after the shower so can keep her warm
After swimming ,hair very dry so must use anti-chlorine shampoo and conditioner.