Second the bodysuit idea along with the float if she needs a buoyancy aid.
For afterwards, invest in a large microfibre towel that will have her dried off in no time plus a microfibre hair wrap. Fleecy, warm sweatpants and sweatshirt and thick socks to dress in should help her worm up again.
Dd has just got the hang of armbands and is desperate to go in the large swimming pool but she's rubbish in the cold. Why can I put her in to keep her warm? I don't want to use one of those wetsuit things as it will make her more buoyant.