There's an easy way to evaluate the quality of a friendship, or any relationship, for that matter. How often do you hear from this particular person? When does she call you? Does she ever check in with you, just to see how you're doing? Is she concerned about your problems? Or, do you hear from her only when she needs something?
Some people are givers and some are takers. Although a taker may be relatively benign, he or she still expects you to do a lot for them, and they'll never reciprocate. Although they're not out to destroy you, it's a one-sided relationship, and you can do much better.
A malignant narcissist, on the other hand, will destroy you. But, first, she'll use you as much as she can. A female narcissist believes you, and everyone else, exist to meet her needs. She'll have you drive her children all over creation, and never offer to repay you in any way. If she doesn't drive, she'll use you for rides. If she has children, she'll expect lots of free babysitting, but never offer to watch your children. (However, this is just as well, because you don't want to leave your little ones with a narcissistic psychopath.)
So, if you "disappoint" a malignant narcissist, by trying to set reasonable boundaries, you may never hear from her again. Or, she will become enraged because you've failed to meet her needs. Watch out. The "friendship" the two of you had will be over, and she will also spread lies about you, in an attempt to destroy your other relationships.
Part of the reason for conducting a smear campaign is probably because she wants to justify her own despicable behavior. Also, malignant personalities are highly concerned with their public image. So they need to convince everyone else that you're bad, and that they have legitimate reasons to discard you as a friend. They also need a cover story if they take it upon themselves to drive you from a job. The workplace, unfortunately, is where a lot of adult narcissistic abuse takes shape nowadays.
Pixabay photo top by Hans