I disagree. And I'll assume on the person being a she - cos she's a nurse - not cos she's got BPD!

I agree that some may not overcome their personality issues enough but the majority of those who have survived a lifelong trauma issue have learned to cope with far more emotional issues than a couple of hissy fitting backstabbing nurses.
The ones who develop emotional management issues later in life are the ones who haven't the skill or experience - or 'mindfulness' to cope with it.

But this particular person made it thru pre-training selection, 3 yrs(+) study and then became appointed to a position - without being flagged?

If she'd gone to a different hospital then recognition might not be an issue - but that's no reason to say she shouldn't work at this one. To treat her differently from one hospital to another for having previous admissions is discriminatory - especially since no other previous (med/surg) patient would be treated that way.

I'd agree with your reservations only insofar as to consider her (potentially) disabled by the nature of her previous psych history - as emotional regulation is a necessary art of nursing that you rightly say can be compromised with such personality disorders. However, given her licensed status - I'd still assume for the better until proven otherwise - as opposed to simply discard the person to the 'do not employ - ever' register.