Shinji Mikami said that Juli is very level-headed and cool in extreme situations, so I don't think at any point she's going to storm off like a brat. Also, Jennifer Carpenter said that Juli is very hard-core.
Here's how I think Juli is going to play out. I think she's trying to prove herself. She's a young female detective trying to build a name for herself in a male dominated profession. She's going to act defensive and tough so that people take her serious. If anyone has seen Resident Evil: Degeneration, I think Juli's character will mirror Angela Miller.
Will Juli be a cliche character, maybe? Then again, Sebastian's tragic backstory coupled with his drinking addiction resulting from the tragedy, isn't exactly the most original idea either. Every character has their cliches, it all depends on how the writer handles them.