This was originally going to be a response post in a different thread, but by the time I finished typing I realized it was better standing on its own.
I have brought nearly every girlfriend I've had balling at some point or another (with varying levels of success)
I learned a few things. The main thing is initiating her gently.
1. Bust out your gun and some empty bottles and boxes, and let her have fun shooting a hopper or so in the backyard. She needs to get comfortable with a gun in a no pressure environment before she is in an environment where she'll get shot at.
2. Show her some paintball videos. Give her an idea of what a field looks like and how players move on it.
3. Go out back out and shoot some more targets and teach her the different playing positions, standing, crouching/powerstance, taking a knee, how to snap shoot and move from each position etc. Let her get really confident moving and shooting and teach her to keep her gun up always and never turn her back to a bunker/the opposing team.
4. Print out a layout and explain the names of bunkers etc so she will know what you're yelling to her (you should stay on her team nearly the whole time). Practice a little bit of communication. Watch a video and have her practice telling you where the players are. In your living room practice a little bit of "Look inside!" "Watch tape!" "Bump!" "Snake/dorito" etc. so she gets used to responding to the sound of your voice. If she can hear your voice out on the field it can be an anchor/comfort to her in an otherwise hectic and overwhelming situation. Your vocal presence will help her keep her cool.
5. Make sure you give her a GREAT mask. Do NOT subject her to beat up worn down barely functional rental equipment, under any circumstances. If your backup gear is not good quality, then let her use your primary while you use the backup. You'll be playing beginner games with her anyways, you can compensate whereas on her first time, she really shouldn't have to. Make sure she has running shoes or cleats, comfortable sweats with gym shorts or slider shorts underneath, a good longsleeve or hoodie, and kneepads if you've got them (volleyball kneepads work great and are $15 at Big 5. Knees are priceless, protect your own and your womans!)
Throughout this whole process you want to be praising her, re-enforcing her progress with loving touch, and making her feel good about herself.
When you teach her to snap shoot, you can be giving her a gentle yet secure hug from behind and guiding her body through the proper motion at first. This will also teach her faster as kinesthetic learning is often easier than verbal or visual. Back off after a bit and let her fly on her own, then give her a high five and compliment her on how quickly she's getting it. Alternatively if she's struggling, practice loving patience and maybe break it down a different way or choose a different and more basic topic that you can build upon when you return to whatever it was that was a sticking point.
At the field, comfort is key! Make sure you have towels and cold water and food. Help her gear up and load up pods etc. Be all podded up and ready for the games ahead of time so there's not the last second stress of running onto the field late and possibly getting split up. You want it to be smooth and easy.
Stay on her team the entire first half of the day. Don't go all crazy Rambo, focus on staying within talking distance of her so she can feel your presence and feels like she's not alone on the field. As she gets more warmed up, you become freer to leave her more distance to play with.
Be really social and talk to people and introduce her to them as your girlfriend. She'll feel proud that you're her man, someone well liked and respected at the field. And now you have all sorts of people who can chat with her and occupy her attention (perfect wingmen) while you go and play an advanced game or two (girlfriend love watching you play and having the opportunity to cheer you on, at least the good ones do. Give her the opportunity to support you the same way you have been for her, by leaving her a bit of space)
Don't play any advanced games with her AT LEAST until after lunch. Then only if she is specifically interested.
Whatever you do DO NOT go against her in the first few games. Even if she's challenging you to, just smile and chuckle and dismiss it, and then if she still wants to, shoot her after lunch
Respect how much she does/does not want to do. These guidelines are the ideal, but not everyone has the patience or the desire to prepare so thoroughly. Respect that, and do as much as you can and the rest, don't sweat it. If she goes and has a great time she may ask you later to show her all the stuff you were going to before, or alternatively if she goes and gets shot a lot that may fuel her desire to become competent at what she's doing. Whatever her experiences and desires are, respect that, and guide her into your world with the loving care she deserves.
This is what I've learned through trial and error over the years about bringing both guy friends and girlfriends paintballing.
I've had girls show up in sandals, get shot in the foot, and drop the gun before wandering off to walk in the forest for hours and pick flowers. I've had one have an absolutely fantastic time until she decided to play a silly game where me and all my friends ran around without guns while she shot at us. Her gun jammed and she got really scared as we all closed in and playfully threw paintballs at her. It wasn't any pain factor it was just having people closing in in an unknown environment.
I had a different girl show up and my two buddies spent the entire time hitting on her while I played. She played some games and had a great time but she couldn't keep up with my pace. I was grateful my buddies were there keeping her occupied and feeling good, even if they were trying to steal her. Don't be offended if people do the same, it'll make her feel good but they don't stand a chance against you
My last girlfriend I met at the field her first time and she was cute so I offered to show her a few tips and tricks.. she then proceeded to charge down the field snakeside and shoot 5 people out. We went paintballing several times together after that. She came to my games and cheered me on and even played without me a few times.
This has been my personal experience in what works, and I hope it helps everyone out there who wants to bring their loved ones paintballing!