Help and advice needed, we are dog sitting for 2 weeks and our new guest keeps snacking at my dog..

[Hoolit]

Hi hope you wise lot can give me some ideas on how to deal with this.

I have a lovely docile gsp, he's never bothered with other dogs ie he goes over sometimes has a bit sniff then goes on his way when we are out.
We have a chihuahua come to stay for a couple of weeks. We've met up prior to make sure dogs got on, on neutral turf firstthen to ours for visit with owner then she came and was left for a day all good.
She's only been here 24 hrs and shes snacking at my dog. My dog is not even bothering her hes walking past or standinghaving a pet and shes on sofa so level with him and has a go.
So far I tell her firmly no, then either put her on the floor and ignore her or send her to her bed.
when I'm out or not about shes in the kitchen like she is at home and my dog is in hall or on landing so no bother there.
Other than this shes been great.
Do you think she'll settle once more used to him?
I'm making sure he's getting a lot of attention too so hoping he's not left out bless him think eeyore then you've got my dog!
Any advice gratefully received but I'm just popping out so apologies if I don't reply straight away.
Thanks

Is she only having a go from the sofa? It sounds like shes resource guarding, I would keep her off the sofa not just put her down once shes had a go.

No shes just had a go when he walked in the kitchen but her bed and food bowls arein there but so are his. She runs at him.

It's not getting any better, anyone??

It's going to be a loooong two weeks unless I get it sorted or I persuade my dm to have one of them!

Can you separate them for at least some of the time with a stair gate?

I have seperated them for periods of time, luckily my dd keeps taking the new one off to play.
I'm hoping she's a little stressed at the newness and will settle but oh the guilt I feel!!!