I prefer bootfoot especially in the sand.Go by your usual foot size.Depending on how much she's willing to spend you could go for the high end Simms for $400+.
Best bang for the buck imo is Cabelas Gold Medal waders.I've had mine for over 5yrs,but I'm also not a hardcore rock hopper either(bad knees).
http://www.cabelas.com/cabelas/en/te...ders&noImage=0
The Premiums are ok but I would imagine they might not last as long.
http://www.cabelas.com/cabelas/en/te...0011367830208a