I have only worked with the Celtic Pantheon. Currently I work with Brighid & the Morrigan.
I know of people that work with different deities from different pantheons with no issue. It’s going to have a lot to do with your relationship with them though.
I feel like you are going to have to find out from Her about that, just because as of recent you haven’t specifically worked with Her, depending on your relationship that could be perfectly fine. Maybe a Frigg meditation to connect with Her.
This is up to you, as I have seen, depending on the reason or relationship with the other pantheons working with different pantheons is possible. As long as nothing adverse seems to be arising from working with more than 1 pantheon, I feel like you should be okay to continue.
Unless something else happened or another situation arises, I don’t believe so. Based on what you have said, this seems more like another deity may have some better insight or knowledge on what you are going through & how to help.
I have not, actually Inanna is a new deity to me! I had never heard the name before.
As I said, I have only ever worked with the Celtic Pantheon. I can say that right now, I do Honor Brighid, but I haven’t specifically done anything with her since the Morrigan came around me. She has her own space, I draw an Oracle card each day that I share with the coven, & “tend Her flame” each day. As far as any meditations or workings though, the Morrigan has been guiding me over the last few weeks.
You may want to look into these too for some other references, advice on the topic as well. I know that @MeganB has done a few topics regarding working with deities & polytheism too.