In I am legend, the vamp woman...?

was she the leaders's mate or something?
because they all got worked up over her.
and is she the only woman vamp in the city?
I only saw male vamps the whole time.

and why did those infected watch will all the time anyway?
and how?

Thats what confused me in the movie.

I was under the impression that she was the Dark Seeker Alpha's daughter myself, due to her age, though she could be his mate too. Whichever the case, he was clearly concerned about her, even surprising Will Smith by trying to save her.

My guess is, female vamps stay in 'the hive', while males go out and get the food, not unlike primitive human societies. Then again, it's possible they were just off screen, or perhaps she is the only one, would explain why they want her back so badly.

The Dark Seekers and their dogs can see at dusk, so they could see Will over time, just never really located his residence until the end.

The Dark Seeker Alpha was rather obsessed with getting revenge at Will for getting his female, even setting up that trap, and later, leading the assault on Will's trap, and again in at his house. He kept the other Dark Seekers from attacking Will near the end (with the barrier), because he clearly wanted to kill him, himself, after seeing the female on the table.

The Dark Seekers weren't really interested in Will's character for food (how much nutrition can they get from one guy), as they can hunt other animals. The main reason they try to kill him, is because he tries to kill them, and later, because he captured the female.

I haven't read the book, so I might be wrong, but in the movie the infected woman had no relationship with the others. They only came to the lab (where Legend--Will's character--was keeping her) because they followed Legend there and wanted to kill him.

They watched Will because he was the only food source in the city. Plus, he kept killing their kind off, so they're pretty angry.

I believe she was just "one of them." They didn't get angry at Robert for taking her, they simply wanted to feast. He was the last man (that they know of) that lives in New York. They were just hungry.