I only remove any dirt (usually on her legs and belly) with warm-ish plain water, then
dry her afterwards. Her
skin is
in good condition generally (though she did get a bit of dandruff during her pre-season shedding session, which has finished now, and her skin is healthy and fine again) I bathe her with a safe insecticidal shampoo I got from the vet, only occasionally during the summer, when she goes in long grass, and can pick up nibbling insects.
Most of the time she gets washed by the rain.