My $.02 as a dad and former swim coach.

Don't ever let her use floaties. Get in the water with her and teach her to blow bubbles, float, kick, go to the bottom and push off, doggie paddle, etc.

Kid #1, we did swim lessons from 3 or 4. It sucked, kids took turns hanging on wall, while one instructor worked with each kid. Five kids in class, so each kid got about 6 minutes of instruction. We did 2-3 sessions. I work very close to the YMCA, so made a conscious effort to take him swimming 3-4 days a week once he picked up basic strokes. He is 9 and swims like a fish.

Kid #2, we did private lessons cheaper than formal lessons for kid #1. A co-worker's daughter is a lifeguard and taught lessons at the YMCA. She worked with kid #2 twice a week for 8 weeks at a lake and she is a very good swimmer for her age, the only kid in her daycare to pass the swim test.

I'd strongly encourage private lessons, followed by time where the child can get in water, pool, lake, ocean over his/ her head 3-5 times a week. A 30 minute lesson once or twice a week will be almost useless without additional time in the water.