It’s not going to ruin them if they take the proper precautions before they get in the water!
Brush thoroughly then put in a tight low ponytail braid. Braids alone can get loose and cause matting as the waves ebb and flow, so I like a tighter pony first with a tight braid. Then wet with non-ocean water and apply leave in conditioner. Then make sure she does a deep conditioning treatment and has the proper professional products to use when getting out, and she’ll be fine👌🏼
Thanks so much McKenzie!!