When my wife and I first met, she was a straight up mall girl and had NEVER done anything off road in her life accept for water skiing as a kid.
That was several years ago.
Now she rides an 05 RMK 600, 144 and knows that where we ride, the trail is for other people.
Getting her to that point took some time and it was fun too.
Her first ride was on the back of my sled and I actually stayed on trail since we were 2 up.
She liked it every where but at the end of the 2 hour ride, I showed her what full throttle on a modified Ultra felt like.
That scared her, but just a little as I only put it there to about 65 or so and let off.
From there, I put her on a little XCR 440 that I picked up.
Took her up the trail about 3 miles to this big play area we call 3 corners.
It's not so difficult or steep to really scare her, so she could relax and sort of learn at her own pace.
The trail circles down around below the area, so it's basically impossible to be stuck in there, (I showed her that part first)
I'd have her follow me down through the area a few times first to have a "road paved" for her to follow, and then did the same thing up ward.
On and off the trail we made so that she could learn what it feels like in a safe place.
We had to go there several times before she could advance on, but for her to stay in it, it had to stay fun (fun = less scary to most females at first)
That last part brings up the whole point to my answer.
Let her learn at her pace and only push a LITTLE,
just enough to help her advance as she's ready.
Have patience.
My 2 last suggestions:
Make sure you have a hot dogger as hot food is nice.
Make sure that she is propperly dressed as being cold and wet will ruin it for her.