Does the same thing happen with males ? I have a female and 2 males, the youngest of the males is showing a huge amount of aggression towards my oldest male. I'm getting really worried.
It can happen with males, but the risk is not near as high as for females. And heck, even though female/male is your safest bet, if there's a serious clash in their personalities they can end up fighting too.
I would definitely advise keeping your males apart until you can hire a behaviorist to come and assess the situation. There might be subtle signs that the dogs are giving to each other that you're missing, and a behaviorist will be able to point it out and instruct you on how to handle it to minimize the chance of them fighting.