We have a 6 month Aussiepoo who was recently spayed. Since then she is acting out in ways she wan't before such as barking, biting, and showing aggression. She even started peeing in the house. Why would this be happening and what do we do about it? We are first time dog owners and have enjoyed her up to this point.

It probably has not a lot to do with getting her spayed. Aussies are naturally dominant, and she may be going through a phase. Has she been through obedience training? If not, you may want to consider starting.

Maybe she is experiencing some sort of pain or she has a UTI.That would also explain the weeing after being trained.
I would take her back to the vet.

I was wondering about a UTI. We also have her signed up for obedience classes. Perfect. Thanks for you input.