Where in South Jersey are you? I know the Pine Barrens are quiet sandy and found it pretty difficult to ride much in that sand. But there are Tons of backroads down there that would make for some great trips.
I grew up in South Toms River and would ride a loop down to Double Trouble State park, out toward the Miller Airfield, and back into the neighborhood. If 10 cars past me on those trips I considered it busy.
Anyway, as suggested above, let her choose a bike. Give her some pro's and con's to different kinds of bikes (MTB, Road, Recumbent). Riding is so much fun.