No worry about your girlfriend. I'm petite (5ft2) and really not strong and had never done any shore diving prior to going to Dahab last February, so was a bit anxious about that too.
Could'nt believe how easy it was. I never had to walk more than 50 ft with my gear on, there was no surge and very little current.
If it really bothers you, you can always chose a dive op that does boat dives (there's at least one in town, can't remember which one though), but shore diving was really not a big deal (at least in Dahab). The only tricky part for me was putting my fins on in the water, but the guide gave me a hand with that. Definitely wear neoprene shoes to enter the water because of the scorpion fish and ursins, and adjustable fins (easier to put on IMO). The dive shops in Dahab can rent you both if you don't own them.
Like el Magnoon said, some dives can only be done in high tide (Islands comes to mind). All the sites have signs showing the entry/exit points, but definitely go with a local guide, they know the area.
Enjoy your stay.