My Chihuahua is a fighter, with my brother’s dog be OK?

@Gibbon no I’m honestly not. I’m just asking so I can understand. And I don’t really think the mastiff could do that to my girl. Could he really? Again my dog knows how to fight, I’ve seen her leave quite a bit of damage before like I said.

@Cuzzzzinkaty I don't know the temperament of the dog I'm just telling you he's capable of killing your dog in an instant. My dog who is a Maltipoo a little bit larger than a Jack Russell and similar build has enough strength to do the same thing but wouldn't because he's not a fighter. However my previous step daughter had a Soft coated Wheatan that was friendly as can be. We had a neighbors cat inside partially feral and quite large that we let in when it was cold and never bothered our mini Yorkie. The Yorkie and wheatan who was much larger played fine together. The wheaten approach the cat and being a stranger the cat caught him across the nose. That dog immediately went into kill mode we had never seen grabbed the cat across the back and tossed into the corner. The cat started to fight back but didn't have a chance as the dog was in full attack mode while I grabbed him as fast as I could and my wife open the door so the cat could make a run for it. Had the cat not scratched him nothing would have happened. He calmed down quick and was back to his playful self. My point is animals of all breeds can be unpredictable know matter how well we know them. 10 minutes later he was out playing with the neighbor kids and the cat was in it's own yard watching and while they saw each other they left each other alone. It wasn't in his nature to fight but she hurt him.

@Gibbon our Chihuahua is pretty strong too. That’s the thing. And what do you mean by the mastiff could shake his head or bite her? Our Chihuahua has a pretty mean bite, and I don’t really understand the shaking head apart. And her paws are pretty sharp too(we need to trim them). You’re saying our Chihuahua can’t kill the mastiff in an instant? She has quite a bit of surprisingly strength., and she moves pretty quick too when she is in “attack mode”