In our last session, a player of mine spent the last 30 min blowing up on me for "restricting" her character's story, and the story of the campaign, when I would not allow her to bring back another character that left because the player left the campaign for personal reasons, and she was unhappy how I had that character leave the game. I explained that I made it that way so that if that player decides to return, his character's return can be as open-ended as possible, and I made the decision to not allow him to return, even if another player plays that character.
I made it clear that it is one character per player. This spiraled down into other issues she had with how I DM, including how I determine what her NPC companion does (which I made clear that I determine his behavior from the beginning), complaining that I'm not Matt Mercer from Critical Role (not that I know what she means by that — the only thing I can think of is that she is comparing my style to his — but Mercer's been DMing for like 20 years and I just started with the 5e Starter Set 4 months ago), among others.
Her background in roleplaying has been involved in MMOs, where her experiences have been almost exclusively one-on-one and completely character involved with little in the way of group dynamics. I've noticed that lately, she has been dominating the roleplaying aspects of the game, from interrupting players talking to NPCs so she can butt in and handle the situation, to cutting into other players' RP moments to develop hers, and I've noticed it has become a problem because the other players check out when she does this.
Additionally, her roleplaying exploits have prevented the plot from progressing and the party from moving forward. Lately, she bullied another PC, forcing him to give her the reward gold for a couple of quests by threatening him with her sword; which, due to me being a green DM, foolishly allowed.
What I want to know is, how should I deal with a player like this in terms of how I should respond to her when she tries to take over the game with her roleplaying, and how to appropriately respond when she gets upset when I don't let her get away with it?
I haven't yet talked to her about this, since this happened just a few days ago. I don't handle drama like this very well and I get very analytical over these situations, trying to wrap my head around it. And that's part of the problem; I don't know how to talk to her about it. From when she blew up, she made it sound that I was responsible for a lot of her frustrations about how the adventure was going; at least that's the impression I got.