The best walking shoes I've had by far are Scarpa Moraines which you can get miles cheaper than the RRP on Ebay. I've 2 pairs one was £33 and the other pair £40 both brand new with tags. In the shops they are about £150ish.
If shes going anywhere really muddy I'd get her boots personally as mud and water can go over the top of a shoe, and a shoe can get sucked off as well! Nothing is totally waterproof even Gortex can fail and you have to keep spraying them etc with Nikwax etc.