But she is fine when she is outside her cage. Two days ago, she found her favorite spot in my bedroom. She would go behind the monitor and stay there. When she is there, she becomes even more aggressive. She bites severely when my hand approaches.
Lovebird hens are very territorial about their cages, particularly mature ones.
It's pretty much the same reaction you would have if a stranger invaded your own private territory. Try to look at it from her angle. This is a behavior that must be accepted because it can't be changed. It's the nature of the bird. She doesn't need a mate to go into this mode.