Oh, dear. Annie dissecting a cat in HS would not necessarily be atypical at all- it may have been an AP Bio class, considering her aptitude and interests. Annie was not the only researcher using animals in that facility. Are you making an implication here?
No, it is not feasible that she would ask Ray for a cat. I just don't have the energy or patience to go through it all again, but animal research is very highly regulated and controlled. If the protocol she was working under specified mice, she would not ask for a cat, she would not need a cat, she would never be given a cat, and she would know that. Any change in animal use would require the approval of a new protocol, which would not involve Ray in any way.
What about if RC wasn't taking proper care of the mice? Wouldn't that impact her experiments? Throw in some kind of "off" variable or something? Or maybe he was goofing around with one of the mice, showing off, and she got angry and was trying to get the mouse away from him, and he went ballistic.