Izzy seems pretty simple to me, she'll hate you if you're not her religion and like you if yours matches. I've never had her backstab me if I'm of her religion, if you go to that hippy 'free religion' nonsense she's not as openly hostile to you but still doesn't really like you. I'd much rather deal with her than with Monty, she's quite predictable and pretty easy to keep off of you if she's the most powerful.
Plus her AI needs some work on tech choices, she doesn't seem to know that her rather nice UU is enabled by guilds and doesn't seem to research it; I've often ended up fighting her horse archers even though she should have conquistadores by that time.