1) easier said than done, but don't fight/argue back.
Kneel down to her height, use a low/calm/soothing voice and say "sweetheart, Mommy does not want to argue with you. I love you." then hug her and walk away and go back to what you were doing.
2) 2 year old kids, do NOT have, fully developed emotions yet. Thus, they spaz out/melt down/get all flustered, They don't even know the exact names for their feelings, nor even know, how they are feeling at every given second.
Like some adults.
3) They are not accurate communicators yet. These skills are not yet, fully mastered.
4) If tired, a Toddler will spin into a melt-down easier.
If hungry, a Toddler will spin into a melt-down easier.
5) Toddlers, want to do EXACTLY what is in their heads/imaginations. BUT they cannot yet do that. Because their motor-skills and appendages and coordination is not yet, fully lucid and able and mastered yet.
Sometimes, the Toddler themselves does not even know what they themselves, want, nor why.
6) Toddlerhood.. .is a time of reactions/cause and effect. They are little mega REACTORS.
They have not mastered complicated premeditated deductive reasoning yet. At all. At this age, everything/their reasoning/reactions... are rudimentary, still. They are learning. The learning curve is either harsh or patient. Per their cognition and per the Parental 'expectations' of their child.
7) Behavior like this, WILL OCCUR AGAIN. They do not have (a) coping skills and are too young to know coping-skills inherently (b) kids learn by repetition even if it is pleasant or unpleasant (c) they are getting their independence streak... coupled with them not having, ANY impulse-control yet. Even 3 year olds do not yet have, fully-developed-impulse-control, yet.
So... in a nutshell. This is phase. BUT it will happen again and is manifested differently, per a child's age. The ages of 3 and 4... are HARDER. So know that.
**(Edit: my son, was SO easy at 1 & 2 years old and the first half of 3 years old. THEN, from the later half of 3 and now at his age of 4.5- it is harder. ) But yes, each kid is different. Just as Linda P. said.
Teach your child NOW... about the names for feelings, how to communicate, that they CAN tell you how they feel, teach them MANY different ways of coping for frustrations, etc.
I began teaching my kids those things, from 2 years old.
My son for example, by the time he was 3 years old... he could tell ME if he was 'frustrated' or 'irritated' or 'mad' and he KNEW the difference for all these emotions and the correct names for it. And then, he'd tell ME... "Mommy I need to sit over there by myself and be alone. I am irritated." Then he'd do that, and then a couple minutes later come to me all happy and hug me and just continue playing like nothing happened.
ALL Moms, have kids that tantrum.
ALL kids tantrum.
They are human.
We are human.
We all go crazy too.
You are a good Mom.
NEXT: where is your Husband in all of this?? HE HAS TO BE HELPING. Too. And since you are pregnant. And since you will be having a newborn to care for.
Delineate tasks NOW... for your Husband to help with.