Swimsuits

Firstly, you need to determine what your daughter likes and wants and then proceed to buy it.
You can show her different clothes in online shops and ask her to choose something she likes the most and something she would like to try on. Online shops are safer because you don’t need to talk to people to order and buy something, and you don’t need to try clothes on and do some actions that can be troublesome. My daughter chose https://the-sleeper.cоm/en/attr-type/swimwear-en/ this way; it is her favorite dress now. I am happy if she’s happy and will do anything for her.

Finally found one. Its a double bonus, it's blue, her favourite colour, it is shorts and a tshirt and she's happy with it. She has tried it on in the shower so she knows what it feels like when wet and she was OK with it. So happy. 

Have a look for wetsuit under garments or surfing swimwear. Can get rash vests (basically t shirts made of swimsuit material) and shorts or some one pieces which have a fully covered back and chest

You could try going for a t-shirt and bottoms style one? I use a long sleeved rash vest and swim leggings or a swim t-shirt and leggings. These are often found on websites for diving as they're more convenient for wetsuits. If still lost, the all powerful amazon is always an option.

There are ones on asos website and next that are long sleeves and cover your full back.