
I would buy two large pieces of Vetbedding (try here: http://www.bedding.demon.co.uk/Mail%20Order.htm )
Cut each piece into two. Put a thick layer of newspaper in the bottom of her bed (assuming you have a plastic bed?) and put the piece of Vetbed on top.
Any wet will pass to the paper underneath, and she will be comfortabley and dry, and it washes well and dries quickly.
This is what breeders use for whelping bitches and puppies, and ensures they stay nice and cosy. You just remove the wet paper from underneath. It also doesn't harbour moulds or smells.