yes it is bad advice as breastmilk is not counted as dairy. Even up to date advice does not advise stopping milk and especially in a baby who is only having milk. I would keep breastfeeding and only give dioralyte on top if you feel she needs it
I think that's terrible advice. If your dd is still not well and you are worried please go back for a second opinion, the rash and high temperature would be worrying me. I think feed as much as she wants, as if she stops wanting to feed its another indicator she is feeling really poorly.