Who is "needy?"
What exactly is the problem with calling a needy woman needy?
“Calling women 'needy' for having needs is sexist -- because can you think of the same-level degrading characterization of a man's needs (for sex, power and women)?”
I wonder what has led you to pose this question. I wonder that because usually when a man labels a woman "needy," it is a reflection of his failure to meet her needs. There are many contexts in which a man comes to call a woman needy, and since you haven't given me any context, I'll just assume that your experience is in a romantic context.
Say you are dating a woman and you are feeling that she is "needy." Every person has needs, and someone's needs are just incompatible with ours or we just can't meet that person's needs by our own volition. An equal and mature approach to women's needs in those cases isn't labeling the entire woman "needy." I wonder if you are feeling insecure because you seem not to be able to deliver her needs or make her happy, hence your question around what's wrong with judging an entire woman by her needs that arose in the relationship.
All humans have needs. But for some reason, a man's needs for power, sex, and women are considered natural; we cannot think of degrading labels like "needy" that we use for men who express or pursue those needs. "Needy" is a sexist term, and I would like to you flag that for yourself.
Last thought on your short question - if you are judging her as negatively, maybe you should not be seeing her, because whoever she is, she deserves much better.
Hope this helps,