Need help

Hi,
I have two Staffies, one girl (3 yrs) one boy (1yr)
My oldest dog the girl has become very aggressive to other dogs since we the younger dog, growling, aggressive actions etc. I have no idea why she has started this behavior or how I can stop it.
She used to be extremely happy dog and would play with any dog but since we got the youngest her personality has changed completely. Both our dogs get on fine also.

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I'm afraid I have not had to deal with aggression but I'm sure other members will be able to offer their thoughts x

Also never had to deal with it - but a few things may help for advise - Are they walked together? Has it just suddenly come on? Anything that can trigger it? How long have you had your boy? Is your girl/boy neutered, if she isn't is she in season?

she is hitting her twenty somthings in human terms and along comes a little upstart. I assume she has been the only dog until the new arrival so expect her to not want to share the fuss. you have to be assertive and let her know its wrong but also make sure she knows there is enough love to go around.
My boy will get the green eyed monster if i fuss his sister but i make sure he gets just as much. and to top it off my girl gets even worse if i fuss another dog to the point of aggression while the boy is cool with it....go figure

I agree with Nathan above it could be a some jealously hitting in. Did the two dogs originally meet on neutral ground ?

Or, does she think she should be protective of her younger pack member ? If it could be this, you need to reinforce your role as the leader. Just an idea.

Hi, thanks for the replies.
Both dogs were met at the rescue center where we got the youngest one from.
I've also had several people saying about jealously/protectiveness so I'm really unsure.
Thanks for the help!

Sorry I cant add anything to what Nath has said, be firm and consistent, they do go through different stages hopefully it will pass

I am know expert but i would say shes either been protective of the younger dog or shes jealous.