Ruby might have prickly heat from the humidity - or a fungal condition. Corn flour works. I use it all the time in the Brisbane humidity.
Yes i agree or flea allergy. Hubby's mums little dog is the only one i have ever seen with flea allergy. You can never see a flea on her but she scratches like mad and gets really sad and will go and hide under the bed. They have her on flea treatment as well as treatment for the allergy's but when she suffers it's awful poor little thing.