Bitch aggression can be one of the most serious forms of aggression and needs to be assessed by a qualified dog behaviourist. Your vet should be able to recommend someone. It tends to happen if the two bitches are similar in strengths and want the same things. These might be the warmer bed, food, owner’s attention, toys, water or even just personal space. It is not something I could possibly give advice on in a few lines without seeing the two dogs interact as the wrong advice could make the situation a lot worse.
Dogs do not live in an equal society and if two want the same things and are competing, one has to defer (back down) to stop the aggression increasing. You will need help with this or one of them will get hurt. Getting them "fixed" is not likely to stop females competing with each other unless its hormone related.
Good luck there is help out there
Rosie Barclay