First thing to check (the easy stuff about soloing an enemy) - is it My Guy Syndrome?
Maybe she thinks that her character would definitely solo that kind of enemy - Goblin, you say? My character sheet says I hate Goblins from the bottom of my heart. Gotta destroy it!
If she does something like that she might just try to get into a roleplaying feeling. It's pretty normal for some people when they start with roleplaying. Some like to do social encounters and speak from the characters point of view, while others love these kinds of backstory quirks that I just tried to demonstrate. Find out why she wanted to solo that enemy. Was is backstory? Did she think she would get more EXP and could become stronger/ more important?
Try to gauge it and steer her in the right direction when you are talking with her privately and don't blame her. Neither of the intentions behind what I just mentioned is bad - but it may be too much if she takes away the other players fun. But then again - if everyone is fine with this behaviour, why not let her be the solo destroyer? It's risky, but maybe she likes that sort of play. Just be curious and ask her
"Hey, just out of curiosity - why did you want to kill that thing so badly?"
Her answer will tell you a lot about her and how she perceives her character and the game in general.
Second thing - make a cheat sheet with the most important rules
DnD has lots of rules - keeping them all in mind can be extremely difficult. An easy thing to do is to give new players a cheat sheet that says stuff like: What actions does my character have in battle? What do my stats represent? If you put that down on a small card and give it to her it will clear up a lot of things.
And don't be too picky about retconning stuff. If she messes up because she thought she always had a Bonus Action and suddenly she stands in front of an enemy at the end of her turn - let her do her turn again. The same with forgetting about Opportunity Attacks and all that other complicated stuff. One or two times won't hurt and she will remember it. If she does it more often she will have to live with the consequences.
You are the only person who can always talk - others have to be silent while you are explaining stuff
It doesn't matter whether you are describing the dungeon, telling someone how Bonus Actions work or playing a discussion as the NPC - you are the one who the players should always listen to. When you see each other physically you could take a stuffed animal or something like that - the player with the stuffed animal is the one who is currently speaking with you. In a chat your software might help you to show the profile of others in different colors or therelike. (Thanks to @KasperVanDenBerg for pointing that out.) That is something that your other players need to learn.
It's unfair to speak when somebody is learning. And you are the one to teach, because you may allow certain houserules and you are the one who knows what's important in your campaign. The others wouldn't want five people talking to them, too - it's confusing and doesn't help. Everyone wants to help, but not everyone can help at the same time. (Of course another player could explain as well, just not more than one person at any given time.)
Being the newbie is difficult
Other people seemingly saying random stuff and rules that come out of the blue... That is environment that is quite weird at first. Far too many rules compared with most card or board games. Getting the hang of it is difficult and you may be a liability for quite some time if the group already got the hang of it. Getting your chance to shine is important. And if she thinks that she can defeat that single pesky goblin and show that she mastered the core rules - you may want to give her a bit of spotlight. Everyone deserves the spotlight, but especially completely new players need it to feel that it's a fun game and they can contribute meaningfully.
If she continues putting the blame for her mistakes on others - booting might be the only option
Talk to her about it if it continues, warn her - and then go through with it. Maybe she will get a grip at the last moment, maybe not. Time's too valuable to spend it with people blaming you for their problems.