"She is not standing."
Translation:वह खड़ी नहीं है।
I had the same question. As far as I can tell, खड़ी is a verb, and therefore, based on what I've seen so far, नहीं would come before it (with an optional है at the end.)
If there's a logical reason why that's not the case, then it isn't exactly intuitive and should be explained.
It's because खड़ी is an adjective and not a verb. It's hard to think of "standing" in English as an adjective, but think of a phrase like "standing ovation", in which "standing" is just a descriptor and not a present progressive/continuous verb. So this sentence is describing the woman by saying that she is in the position or in the state of standing, as opposed to saying that she is actively completing an action.
Replace खड़ी with another adjective like छोटी and you will see why नहीं then is coming after the adjective (and before the verb होना):
वह छोटी नहीं है। - She is not short.
Because here हैं is the verb which is being negated by नेहीं, the final हैं can only be dropped when it's something else which is negated.
That's my understanding anyway. Note also that native speakers seem to 'slur' (for want of a better word) nehin hai together, so it sounds more like ne'hai, or so I've noticed in films etc., so it can sound kind of like it's been dropped even when it hasn't (if you listen hard/in the speaker's mind/if you turn on subtitles).