I would start off pretty easy and just try to judge how good her riding is. I took my girlfriend cycling once and went for a rocky descent 🙂 She crashed only once but I don`t think she enjoyed that too much.
Next time I took her riding again it was in Glentress and did only the blue trail with her and she liked it a lot, not technical, quite fast and nice scenery.
If she is not going to enjoy it then probably will not go out cycling with You again 🙂 I would go for the easier option and some techno (yeah) bits just to spice things up and not make it boring.
After that You should know how good is her riding.
Other problem I found with my girlfriend (but she might be the only one that does that) is that she could not judge the speed to enter a corner properly or ride over some sections, so that is why she came off that one time. So next time, knowing that, I was riding in front of her keeping the speed down so that she could nicely keep up and still enjoy the ride.
She is a lady, treat her nice 😉