Okay, I've finally gotten my callbacks.
First,the vet called. He had been in appointments all day and did not get to look at Lola. I explained the whole situation to him and my concerns about Paisley's possible aggression toward humans. I told him that, while up at his office on Saturday, one of his technicians asked me "What are you going to do about the other dog?" I told him that I had responded to her "What do you mean?" I told the vet that she had implied that I needed to figure out what I was going to do. The vet got a bit testy with me (which kind of bothered me because he's never like that). He said "Are you telling me that this woman asked you if you were going to euthanize your other dog?" I told him "No, that is not what she said but it is what I gleaned from her tone." He then told me that I must be mistaken, he has known this woman for years and she would never say that.

Okay, whatever, we moved on.
So, he tells me that dog-on-dog aggression does NOT automatically lead to human aggression and he thought it would be ridiculous for me to even *think* about putting Paisley down if I felt comfortable with how she is with people. You know, I don't even think he would do it. We then talked about what may have happened in the yard. He is going to do a small autopsy on Lola tomorrow just to try to confirm what kind of wound she has so that I can get some kind of answer but he said we will probably never be able to know what/who did this or if it was Paisley.
Shortly after that, the trainer called and I went through the whole thing again. She had a LOT more explanations for what could have happened between the two dogs. It will be hard for me to explain because I don't remember all of her terms, but she said that there is often an issue with having a larger dog and a very small dog. The larger dog often doesn't interpret the smaller dog as, say, a "real dog" and can often view it as prey. Usually this doesn't happen, but sometimes an instinct will kick in for some reason and the larger dog loses it. She said they very well may have be tracking something together and Paisley's hunting instinct turned to Lola.
The second issue was something called "predatory something or other" (sorry). She said that a dog can be sitting in the yard minding it's own business and the other dog could be at another point in the yard chasing a ball or just running. If the one dog kind of "catches" the sight of the dog in it's peripheral vision, it can kick off some "predatory prey" instinct and the dog will immediately kick into hunt mode.
The third issue is just having a dog that doesn't like other animals and is threatened by them. She believes that option #1 or #2 was probably what happened. She thinks that if #3 was the issue we would have had tons more problems.
It seems that the biggest problem was Lola's size coupled with the fact that Paisley is a hunting animal.
I told the trainer that, for my own peace of mind, I would like to have Paisley evaluated for human aggression. She said they regularly do this and it takes about an hour. So I have an appointment this Thursday afternoon to have that done and I guess I'll see where we go from there.
I somehow thought I would feel better after hearing from them, but I guess that was a bit too hopeful. I still feel like crap but, at least, I have a plan now and I suppose that will get me going.