My girl is fine with smaller dogs, the neighbor has a Pomaranian who's become my girls best friend. She usually plays gentle with smaller dogs, she does tire out before they do, so she just comes home!!!
I have only had one incident in her two years, and it happened two weeks ago: I was walking Sunshine down the street and a guy with a Shar Pei comes up to us, wanting to meet and greet ...well, Sunshine comes up slowly to sniff and smell the smaller dog. The Shar Pei snaps at her and Sunshine backed away, she again tried to slowly approach the smaller dog, as if saying, It's cool, only want to make friends...but again the Shar Pei tries to take a bite and Sunshine just backed away...The third time the Shar Pei tries to take a bite at her, Sunshine got PI>>ED!!!,
Now, keep in mind, in two years of owning her, since she was 8 weeks old, we've never, EVER, seen Sunshine get angry or agitated, she's been harrased by little kids, little dogs, big dogs, annoying relatives, you name it, but this Shar Pei just ticked her off!!!, because she immediately snapped back at the Shar Pei, the smaller dog ran and took his owner (via the leash) to the ground and dragged him a little...I think he was embarassed about it, (his dog was being overly aggressive) ...and I was taken aback, see, if Sunshine ever wanted to break that Shar Pei in half, one bite would do it...the little runt knew it too....
Overall, I think she has a FANTASTIC disposition, but just like people, sometimes she just has enough!!! so I always, always supervise!!!