Hey WOI,
Great screen name!

It's a good reminder to yourself that you are indeed "working on it", since you can't depend on your pwBPD doing so.
It's not a surprise that you will get tired of working on it - don't be too hard on yourself.
Setting a boundary and leaving to spend some time away is fine. It's one of the skills. For best results, hopefully your aren't just going off and doing your thing after a fight.  :)o so when there no fight on. But its probably important to tell her when you are going to do so - even though it can cause her distress. To the extent it does, employ another skill - validation - when she raises concern about your "new approach" to looking after yourself.
I guess I am saying is try not to go "No Contact" as you begin to look after yourself. Talk to her - as triggering as that may be.