Thanks for all the helpful tips and responses! Keep 'em coming if there are any others! Good ideas taking it slow and introducing one thing at a time - I think that will help a lot, especially with our little one.

She is working hard in the pool every time we take her, basically teaching herself how to swim at this point, all she wants to do is practice and challenge herself. She swims with goggles, so replacing with a mask should be a minor adjustment, then getting her to use a snorkel should hopefully be a fairly simple step up. Thanks again everyone!

We're thinking of giving these a try. Looks pretty comfortable, we'll have them wear long sleeves whenever we go snorkeling, and you can add or remove flotation depending on skill level and comfort.
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Great tip on simple break signal as well.