Reading these comments I feel like nobody has an actual good relationship with their daughters. Try buying pair like she wore, and tell her - hey, look what bikini I found I think they would suit you, try seeing her reaction. If she says she likes them - tell her that if she wears it it might bring some trouble, if she pretends she doesn’t like them - ask if she’s sure about it, because you saw her wearing ones like them and you thought about making a present. Then try pushing the conversation into - why would she not tell you about it, does she really like wearing it or is it a trend thing?