I'm sorry to read about this.
Now, we've had a few scuffles happen over at my dads house with the 3 dogs. Over a year ago, I was doing tricks with the two boys (and giving treats obviously) when Lilly, the JRT, came from about 10 feet away and just went AFTER Jackson. Now Jackson has never started a fight but he surely will finish one so he was fighting back... in the process of pulling them apart, Lilly latched onto my boob (yes my boob!) and I had a nice pretty scar there for 2 months. The second big fight was a few months ago when Buddy and Jackson leaped down for the same bully stick at the exact same time and just went at it... it was really surprising because those 2 had never done that before and they really love each other. Lilly, I could understand, because she's always a b*tch, ha. Jackson had a little scab on his ear from that fight.
But here's my question... how many other times has Sadie full on fought Bentley, ever like this? Dog aggression not does automatically equal human aggression... but if she's FOOD aggressive, then yes she very well could do this over a piece of food the baby drops. Not wanting to scare you. Can you take a bone from her, or a piece of food, without being bit normally? I'm unsure if she's more dog aggressive or food aggressive so if you could maybe explain more.
Either way, since she is so unpredictable, I would be proactive in only feeding her in a crate or another room. No treats with the two of them loose, things like this, etc. Resource guarding is a big issue that needs to be trained and kept under control. However if this was just a one time thing... dogs will be dogs and fights will happen!