Vagsnatcher

Female version of cockblocking.

i.e.
1) The close friend of the male that the female is trying to get at causes the wanted male to declare the female off limits as to not ruin their friendship.

2) When another female comes and begins to flirt with the wanted male.

3) When an unwanted male who has repeatedly made his interest in the female evident and was rejected cause and intervenes and stops the unwanted male from approaching the female through either spreading rumors or being obnoxiously clingy.