This is actually really difficult and it shows how few very good beach resorts there are in Europe. The West coast of France has great sandy beaches (but the weather could be poor). Have you looked around the Ile de Re? Very chic and very French but you would probably have to compromise in terms of a luxury hotel. Your daughter would be well looked after everywhere you went though.

The other place I think might work is the Algarve. Again, very good beaches and slightly less ruined than the Spanish costas (although still not great), but I have no idea if there are any decent hotels. How about hiring a villa near the beach?

Good luck!