I am in such a situation currently. I am married, not currently seeing anyone while my partner is seeing someone he has been enjoying for coming up on a year now.
In working on myself to get better at poly, I have learned that when I am triggered I can't just stop at whatever BAD FEELING and take it back to last time I felt that way. I have been working on all the times I have felt that way and ran smack dab into some seriously unaddressed and nigh buried scars. These are the kind that I cannot do work on without feeling those moments all over again. It has had me at times flooding and freaking out but not shying away from what those moments caused in me anymore. I'm not working on getting better at poly anymore like I was initially. I am grateful to trying poly for the way it has brought my real issues to the forefront. And I won't kid you, what I'm going through splashes all over my primary and his GF's relationship. I do see that but it will only stop when I have put in an amount of work that makes my primary relationship stronger and me more healed.
I can only hope that the amount of time it takes me to work through this stuff stays in a time line that results in a brighter association for us all. She is growing impatient and talking to him about exactly what you're worried about.
It might sound pretty crappy to her and maybe will to you but to me and to my partner, preventing her inconveniences through this are low on the list in the face of what getting through this means to us and our relationship. I can only go at the pace that works for me. It is work I already have to push myself to do because its not fun, it IS disruptive to my life and my relationship let alone how it inconveniences her now and then. I've ran from dealing with it for 20 years already. How it inconveniences her isn't going to have me putting it aside. I cannot as she can (she is married), go home to my primary relationship for comfort when I am already struggling within it. As someone's primary, she should get that or move on to someone who doesn't have a primary partner at all or one not dealing with what I am working on.