Baby IG with older miniature Schnauzer

Hey!

We got a little IG (boy - Lenny) yesterday. He's 12 weeks old.

We also have a 7yo mini schnauzer (girl - Heidi)

It's a bit tense at home. He have given Lenny a separate area, but when he's out with the other dog, she goes for him. Not done any damage but it's a bit scary

We've read you give them 5-10 mins to socialize and when they kick off we separate them. Any tips?

I've got more questions on house training him - hard to make him wee outside when he hates it 🤣 - but can deal with that later

Thanks