I had a google after reading your post and found this
http://nh.craigslist.org/for/894953516.htmlif the dog isn't a giant breed, and as it's a girl, maybe disposable baby nappies could be used ? - with a hole cut for the tail of course ;)
this page has a few items which look interesting
http://www.canineconcepts.co.uk/item--Disposable-Dog-Nappies-Diaper--dog-diaper-nappy---dogsIf she is already a little sore from being wet, sodium bicarb (about a tablespoon in half a washing up bowl) in the water she's washed with is very soothing and will promote healing. I used it when one of my children had severe nappy rash and it worked like a charm!
To protect the skin from more wetness,
WAITROSE - BABY BOTTOM BUTTER is very cheap, highly effective and made from really natural ingredients - it's amazing stuff! and it smells like vanilla :)
Hope this helps