I've never quoted myself

She also might surprise you and have S5 ready for you at the agreed upon time.
I'm so glad the transition was drama free for you and S5. What a relief!
This suggests that validation and other skills may be helpful in the years ahead. On this board, we tend to go straight to boundaries because the conflict has escalated to the red zone. Going to court is primarily about negotiating boundaries with the legal system, in the hopes they will be regarded by the BPD parent
But she may also be responsive to validation and SET (support, empathy, truth). Did you have an opportunity to use those with her during the relationship?
Once you get the court orders in place, she will most likely continue to test boundaries. By then, you may find that the skills help de-escalate unnecessary conflict. It's possible, tho a bit harder to do that now because there is no clear authority, which is a much more inviting environment for her to color outside the lines based on whatever mood she's in.
Hope you and S5 are having a good time, and that you had a chance to restore some strength and take care of yourself during the break.