Bridge cameras look and work very much like an SLR but you can’t change the lens. The lenses normally have a good zoom on them with an extra digital zoom, but this is where the image quality can suffer.
If she has a Nikon 35mm SLR now, then getting a Nikon digital SLR should mean any lenses she has for the 35mm will also fit the digital, saving the cost of buying new lenses. 