I once went with a friend, or someone who I thought was a friend to a “non-denominational Christian” service. It was an ambush. Im not suggesting that your situation is at all. These people were mean. They had an American flag in their "sanctuary because everyone else was “worshiping” the cross according to them.
I am not going to repeat everything else that went on as I am now going to rebury the experience back in the trashcan of my memories. I am sure that my experience would be totally out of context for yours should you go, but seriously, this stuff plays with your head.
I would rather have oral surgery than go. You don’t need to tell her that

but you can tell her that you want to be honest and say SDAs have been critical of your faith in the past and you feel very uncomfortable with putting yourself in that position where you will be for all intense purposes, a captive audience. What if you are introduced to everyone has her “Catholic friend?” What if there is an alter call? That happened to me at a "Christmas choral service I was “invited” to. The were going pew by pew and asking questions during the service. I got up, made sure that everyone could see that I was getting up, and walked out.
“Just say no.”