My sister has bpd. At her best, she is kind, generous, loving, will do anything for you, hilariously funny and loyal. At her worst, she is aggressive, dramatic, pessimistic, suspicious, paranoid and constantly seeking validation. In past relationships (which have all been long term) she has often found herself with someone she thinks she can fix - either someone with a chaotic lifestyle, or lonely, or with a mental health condition of their own - and devotes herself to them, smothering them with love and not wanting them to be out of her sight. Inevitably they have all felt suffocated by her and their own problems have meant that their own wellbeing is best served by extricating themselves from her.
She has been with her current partner for 3 years now and apart from a few anxiety attacks at the start of the relationship about the dp's feelings for her, she has transformed. The difference is that this partner is an equal to her with no chaos in their lives, happy family background, same age, similar interests and crucially the ability to stand up to her and tell her when she is being too much. If you met her, you would not know about her bpd these days. She hasn't self harmed since meeting her DP, when it was a regular feature before, with her hospital admissions being frequent.
The right partner can really make a difference in how a person manages their bpd and the fact yours has suggested time apart to help her deal with her feelings is a positive one in in my experience. It means she isn't reliant on you for validation when she is low. My sister has gone from attention seeking behaviour when struggling (holding a knife to our mum's throat, taking overdoses in front of a partner when they don't want to do what she has planned) to being content when her partner is at work or out with friends, and not panicking that they will leave her when they tell her she is being a twat. Good luck!