I'm in a similar situation. All my guns don't suit my GF. And she is loving everything I hand her. Rifles are one thing, but shotguns point and don't aim so now I'm in uncharted territory. I grew up shooting what dad had so I've adapted my technique I guess. Having watched lots of YouTube and doing other research I've realized my technique/mount is as just as wrong as her's when I'm looking in a mirror.
From this information I've drawn 2 conclusions:
1: a shot gun doesn't have to fit to be a hunter/competitor if you are casual and can shrug off a miss or some pain as "typical"
2: it's damn important if you want to not scare off your son/daughter/spouse/pastor from returning to the sport
So my recommendation is this: Find a clay competition in your area that has some female competitors, introduce her to them, and be ready to spend $2500 to make her happy.
Unfortunately I'm 6,0" 205LB... I can buy any shotgun I want for 45 cents and shoot trap until JT says its scary; however, my GF is 5'8" 160LBS and cant shoulder my 8+LBS doubles with full power 3" steel loads.
My GF just signed up for her PAL and I'm buying her an O/U for graduation (don't tell her its a surprise). Luckily I have the means to do major modifications to it. However it will resemble a Syren Tempio Field (at least in dimensions) when I'm done.
One other thing I can tell you about reading about female shotgun shooting is don't fall into the 20/12 gauge trap. From what I've read, they prefer the 12 because the weight actually helps the recoil. Worst case load her some 12ga 7/8oz loads.
You love her, let her tell you what she wants you to buy her, engagement ring, or scatter gun, she deserves the best you can put in her hands.
Edit: I've taken a bit more of look through the thread and it looks like you don't want to drop a lot of cash. You have to consider who the typical off the shelf shotty is marketed towards. She's not the average right handed white male. So if she's dyeing to shoot, hand her one of your shotguns. Do your best to raise the comb and teach her about proper "tight" shoudering. Make sure she is aware that it might be uncomfortable but that is because it's wrong for her. I think if she is reasonable she'll understand that it only gets better from here (because you are going to spoil her with the perfect treat

. This doesn't trump letting her talk to other females about their experiences. They have a lot more learning curve than we have lets just face that right now.
I remember the first time i shouldered a 12ga... it was a 3" steel HV shell in a cooey single with a 2.75" chamber. I was assured it was no problem shooting that pigeon in dad's hay barn. I swore I'd never do it again, but here I am 20 years later, teaching my GF to accept recoil as part of life. It could just be that some people enjoy it and some don't too.