i think you need to be prepared for wild swings of behavior...between the best behavior youve ever seen from her, and wild fears, anger, blame, that you will leave again.
things are likely to settle down, but it could be pretty hectic for a bit. listening, letting her get it out, as well as empathizing (not apologizing for) with how she would have felt/feels now, will go a long way.
The other rub is I booked a trip out to see my brother next Tuesday. She doesn’t know about the trip since I expected to be detached when I was to depart.
this will likely be a biggie. you will need to tell her (postponing it is another option, and a good one if viable). she will want reassurance, probably even unrealistically so. check ins and such will be necessary, you can set those up in advance.
it sounds like youre definitely thinking this through. whats her beef with your family?