Seems like you're just not looking at it from Ellie's point of view.
If someone had been constantly lying to me about something that really mattered to me, even I'd be f**king pissed. Add to the fact that that thing happens to be something that is unique to her and has the potential to save the whole f**king world. It's like a super-hero having a super power and not being able to do anything with it. When you have something like that, you want it to matter and to have some purpose. Heck, people even without superpowers want their life to matter and have purpose in some way. Joel snatched that away from her.
Now, most of the deaths that have been happening in the world are on her and on Joel. This is shown in that Hotel segment in one of the flashbacks where they find that dead couple. That feeling of guilt keeps adding up. At least Joel got to make that choice for himself where as Ellie had that choice taken away from her. Not saying that Joel was wrong in what he did. That is why these characters are as good as they are. Conflict has been created without having the characters stray away from what makes them true to themselves.
Joel had his reasons for what he did as Ellie herself comes to understand but forgiving someone can still be hard. That's her whole arc.
Also, why do you find it strange for her to be pissed off on Joel and then directly going into revenge mode? It's pretty clear that she still cares about him. People can and do get pissed off on family members and still care about them.
And she behaves like a confused teenager because she is a confused teenager.
As much as I like Joel, I'm glad they didn't do that. If they had, this game would probably have felt like an entirely separate chapter, just with the same characters.
Now because the plot of this game and also Ellie's whole character arc take off from the implications of what was done in the first game (in perhaps the best way possible, I might add), both parts feel like a whole.