aggressive boxer pup

Question
My in-laws have a boxer puppy around 6 months old.  She's been neutered.  Lately she has become very aggressive toward
other dogs.  I'm afraid to bring my own boxer puppy (4 months old/not related) around her. The last time my puppy was around her she attacked my dog, luckily my dog was OK.
The 6 month old boxer lives with 3 other small dogs and she is beginning to get aggressive with them too.  She lives on a farm and is chasing cattle and horses and seems out of control. I don't think this is typical boxer behavior, my own boxer puppy never behaves like that.  What can my in-laws do?  They were told by one obedience school that they should wait till she's a little older to start working on this problem, as if it's just a puppy thing. Then I worry if she will become aggressive toward the children too.  We all love to go to the 'farm', it's a great place for kids and animals to play but this aggressive puppy worries me.

Answer
6 months old is young and both old enough to train NOW.

The obedience trainers are incorrect.

Training should begin the moment the puppy walks and plays.

They learn by sight, sound, taste, smell, touch, and association(s).

They should leash the puppy in training outside and get her used to the leash and that the owners are the "alphas."

Pull on the leash with verbal commands to stop, or no, or whatever she is misbehaving over-- keep verbal commands simple and in a commanding voice.

Give her a treat for obeying and good behavior. Cheese is a good tidbit.

Gradually allow her to run loose and when she misbehaves- use those verbal commands they taught her. When she behaves, love her and give her praise and a treat. If she does not obey, then they need to come up with a reprimand. A time out inside away from the family, or inside a crate for 5 minutes.

In about 3 weeks of this training she will associate good behavior and obedience to praise and attention and a treat. And associate not obeying to a time out and possibly isolation.

Try that then socialize her with your puppy using the commands she's learned.