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.
As for zoom, my one has X42 manual & then X2 digital, the moon picture above was taken at X84 (X42 + X2 digital), A tripod was used & a remote shutter release. Digital zoom has come a long way, see up loads.