Thanks everybody!
CP, I'm really not sure what caused it. Mollie and Izzy generally do not interact with one another at all. I also don't think that Izzy would start anything with Mollie over nothing. My mom was cutting up a mango so it could have been food related but Izzy and Frodo are the ones who tend to scuffle over food, I don't think Izzy would attack Mollie just over food.
My best guess is that Frodo started acting like an ass with Mollie when the food was out (he'll try and block her and he'll growl, but he'd never actually start something), and Izzy went after Mollie? I don't know, I just don't see Izzy going after Mollie in that scenario unless maybe Frodo somehow elicited a vocal response from Mollie and that set Izzy off.
I really don't know, in case you haven't figured it out, lol.