Thanks for the advice everyone.
I ended up bringing the following:
Marlin 795 .22lr carbine
S&W 22a .22lr pistol
S&W M&P 40 full size w/ silencerco osprey
S&W M&P 40 compact
Noveske N4 14.5" AR-15
We started out with the 795 and she really liked it. We started at 7, then 15, then moved out to 25 and she had no problem hitting an IDPA silhouette at those distances. Next we tried the S&W 22a, she liked that one a lot too. I'd say she liked the 22a best of all the guns we shot.
So then I had her shoot the AR-15. I explained the basic operation of the rifle and had her watch me fire a few shots. I adjusted the collapsible stock to best fit her and explained the proper stance. She fired one shot then put it down and said she didn't like it because it was too heavy in the front (it has an sws free float rail) and it hurt her shoulder. Honestly I think the noise from the 14.5" barrel was what bothered her more than anything.
Next she tried the M&P 40 full size, without the suppressor. I explained how to operate and hold the pistol, and changed out the backstrap to the small size to best accommodate her size. Again she fired one shot, then put it down and said she didn't like it. The muzzle flip for her was pretty extreme (i.e. the muzzle went up about 45-60 degrees during recoil) despite my best effort to explain the proper grip. I think she just wasn't gripping it hard enough.
So it was no problem, she shot about 100 rounds of .22lr between the S&W 22a and Marlin 795. I fired a few magazines through the Noveske AR-15 in between her strings of fire. Eventually we went out to check the targets; for some reason she wanted to put a birchwood "sticky" on the "groin" area of one of the targets. I said OK then she said she wanted to shoot the groin with the AR. I said fine and she picked up the AR, fired about 10 rounds through it and hit the 8" paster on the groin about 5 times at 25 yards.
All in all she said she had a fun time and thanked me for showing her how to shoot. She seemed to enjoy it, but mostly liked the .22's. We didn't even try the 40 compact and to be honest I only brought it out as an option because I was carrying it as my CCW anyway. I was glad she showed some interest in the AR-15 toward the end of the range session. While she was firing at the groin I had her use a bench rest instead of shoot freehand which she seemed to like better.