RE: Board for my girlfriend
Having your girlfriend try wind surfing, and like it, is indeed exciting.
Perhaps get her a smaller and lighter rig (something you can use when the wind is too strong for your 6.5m2 rig) and she can progress nicely on your GO 190 ltr.
The nest step for you would problably be a Carve.
At 90 Kg, it would seem the Carve 122 or 111 would compliment your GO 190 pretty well.
Also, you may need a larger rig to extend your range with the Carve and GO to a little bit less wind.
Hope this helps,