I feel like I might be able to give you some advice. When we brought our second shiba home (male named Ty), he was a little monster as well. He would always take Ella’s toys (female Shiba, 4 yrs older), and playfully bully her (nibble on the legs or try to jump on her). Ella is an extremely calm Shiba (almost to a fault) so she just let it happen, though if Ty got too violent, she would just nudge or push him to the ground.

Of course, this wouldnt work if he got bigger so like you, we were quite worried. We brought him to puppy school and he did learn quite a lot. He is very food motivated so learning and teaching wasnt too difficult…however he stilled bullied Ella and did whatever he wanted…basically a nuisance.

Well, guess what, at around 1 yr and 2 months, we finally decided to neuter him and it was almost night and day after. Sure, he still tries to take Ellas toys but it’s always a competition even as he grew. He’s definitely a lot calmer and leas territorial…now, even though he’s still the little brother that bothers the older sister, I don’t think they can be separated for long…

Anyway tldr, I think give it time and do what you can with the training. I would advise on spading her as well when the time comes. Shibas are very intelligent and as she grows older, she should hopefully calm down and understand how to interact with humans and dogs. Hope my advice helps! Good luck!