Hi & welcome to YT. You've gotten great advice so far and the new food is a great one. If you switch over all at once, she might get diarreah. It is recommended that you add the new food gradually to the old food until it is all new food (over the course of 1-2 weeks).
You asked about her swimming. There are lots of folks on here who have pools and their Yorkies love them. Just make sure she is safe when swimming just as you would a child. Never leave them alone and make sure she doesn't have access to the pool when you are not around.
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