I took my girl friend out last year for the first time. Here was my experiences:
3 weeks before the season we got permission to a property where we were constantly seeing birds. Every morning before school, she would take the extra "long" way to school to see if they were out and in the fields using the same patterns. Luckly they were.
Around that same time I had her get comfortable with her 20 gauge and turkey loads. 10, 20, 30, and 40 yards....learned really quickly that her range would be 30 yards and I wanted her to see why.
The night before our hunt, I snuck up to the area we constantly watched birds with a pair of binos....I had located an area on Google maps along the river where I believed they would roost over the river. Luckly I was spot on and when I lifted the binos I could make out a dozen or more birds in the trees over the field I planned on setting up in.
The morning of the hunt, I carried in as much as I was able to and made sure everything was comfortable and perfect. Long story short, the birds started to gobble and she immediately started to shake. I knew we were in trouble when a bird came in if she was already that excited. Luckly scouting paid off...4 jakes pitched strait into the strutter decoy. I coached her on getting her gun up and after watching her barrel bounce bird to bird I made her concentrate on 1 particular bird by telling her to shoot the one with the red head. shortly after that....the jake laid there motionless. 45 minute hunt.
She now has the itch BAD. Killed 3 deer this fall with bow and muzzleloader but is itching for turkey season to get here. She will chase them with a bow this season and has been practicing every day on a mouth call trying to learn "the way".
With that being said....A.) Do EVERYTHING you can to make sure she is comfortable. If you are able to afford a blind, get one. They will make things 100x better. Conceal movement, nerves, and instructions.
B) as others have mentioned and I mentioned....scouting will pay off big time! There are areas that birds will go to in certain events. (i.e. Raining, sunny, windy, etc) Find those areas and you will be GOLDEN.
C) If you can, get a decoy or pair. Better yet if you can afford it DSD's, but any decoy should help. Again it should help draw the attention away from you and her and may help you get away with a little more.
D) Make sure you know your affective range, and watch some videos. Reading a turkey's body language and vocals may make or break a shot. Videos will help with that, but more than anything personal experience will help the most. Wait for the neck to stretch out (do this though a cutting on the call) tell her to put it on the red waddles and watch him roll over.
E) Patients is a virtue. I've messed up so many birds I can't count from getting antsy. You will be with her and running and gunning is a better solo tactic for most parts. She is your priority and your scouting should have you in the correct areas. Remember a bird after 9 or 10 pm that gobbles is a LONELY bird and will come 9 out if 10 times. Stay put and call to him every once in awhile, however keep this in mind, a lof of turkeys will stop every time they gobble....and the more they gobble, the better the chance is that a hen will intercept him and he may never come.
F) Practice your calling basics. Yelps and cuts will get you a LONG way on a slate call. Dont think you have to be a pro on a mouth call to kill birds.
G) LASTLY....HAVE FUN! make it a memorable event for the both of you. If you kill a bird or not, your spending great time together in mother nature and learning things together. Embrace it