Your are risking something terrible.
I have bitches. Once or twice I have been less than perfect when latching a gate, and when I came home two were together. Two that shouldn't have been together! But, they did nothing to each other until I got home, and two greeted me at the gate instead of one, and then it was on.
Because bitches can be VERY jealous of us.
I would never intentionally leave adult bitches who have a history together. Up to now, fights have started because they both came up to you, whatever. But when bitches have a history, all that has to happen, is one bitch bump into the other walking by and then it can be ON.
And if you aren't there to stop them, bitch can and often will kill each other. You come back to a bloodbath with one dog death and one needing to be euthanized. It is a horror story.
Up to now, you did not know this, but now you do and if it happens, now it is your fault for not taking heed of clear warnings. I know that is harsh, but the consequences of leaving these bitches can be devastating. And even if one doesn't die, but kills the other, will you be able to feel the same affection for the dog that killed your other pet. Maybe the young one kills the older one, will you be able to not anthropomorphize the situation and completely exonerate the bitch as though nothing happened?
Heidi Ho, Odie
Joy-Joy, Bear Cub, Hepsi-Pepsi
Cujo2, Karma Chameleon
Ramona the Pest, Kojak -- who loves you baby?
Tiny Tinnie, Susie's Uzzi, Kaiah -- The Baby Monster.