As others have said taking a pillion is a different skill to riding solo, SMOOTH is the key.
Also riding on the pillion is a skill,it takes practice.
I have been riding for 40 plus years , but am a terrible pillion 'cos I rarely do it.
If you are worried about her coming off at 80,slow down to 70,at least till you become a "unit" on the bike.
I used to ride as primary transport ( no car ) so previous girlfriends got plenty of practice and got used to my style of riding, to the point they would anticipate me, but that is a two way street,ultimately the pillion should set the style ,the rider adapting to them.Then they could move around on the back to get ready for the upcoming road situation,closer for twisties,back for boring bits or whatever, knowing that I wasn't going to pitch the bike around at a certain point.
When that happens , everyone relaxes and gets comfy , and it becomes enjoyable for both.