Can female guinea pigs be aggressive?

Yes! They are very friendly. but like all rodents they do bite if you put your finger in front of his mouth. It is because of this they are highly recommended for young children who want a pet.
It depends on a guinea pigs attitude, Really. Mostly they are very friendly, but if you put two guinea pigs in one cage they do become aggresive. Try not to place two male guinea pigs in one cage.

Personally I think guinea pigs are the friendliest pets ever!

(once they get to know you.)