If you can find it anything by Andrew Blake. Night Trips 1, and 2, House of Dreams, and Secrets are all good. They were made in the late 80s early 90s so they're a bit cheesy but all very couples friendly.

Honestly though you know her tastes better than anyone so it's up to you what you pick. Besides research has shown that while women claim not to be turned on by the hardcore stuff their physical reactions (wetness, body temp, respiration etc.) tell a completely different story.