* classes * the swimming pool

I'd also split the sentence: I certify that Noelia takes swimming classes three times a week. She is a good swimmer, she is not afraid of water and she can swim properly in the swimming pool. It's not incorrect as you have written but in this case taking swimming classes doesn't necessarily mean you are a good swimmer, so I wouldn't use 'so'. Splitting it makes you sound a better swimmer and has a more formal tone.

I cirtify(confirm) that Noelia takes swimming class three times a week. she is a good swimmer and swim well being not afraid of water in pool.