Well my brother’s dog be able to handle mine?

My brother has a 250 pound English mastiff, I haven’t been around this dog too much, but I’m curious how similar his dog would be to mine? I have a toy Chihuahua who loves aggressive play. Will my brother’s dog be able to handle the Chihuahua? She can really be quite dominating in terms of strength and temperament when playing.  she is a very very sweet dog but when she plays she loves to play like rough and tumble. And she honestly can really stand her own ground. My girl is pretty vicious (she is just playing).

For example when she has a rawhide in her mouth we know not to mess with her, and when she has a chew toy she absolutely obliterate it, throwing the toy across the room with stuffing everywhere. She really can hold her own, don’t even get me started when she plays tug with other dogs.

Also why are people saying that the mastiff could easily hurt or kill my dog? Couldn’t she do the same to him? I really mean it, she can hold her own ground and let other dogs know that she needs business. Believe me, my girl is a fighter.