Congratulations!
From a woman's perspective there are a couple of things. When I had my first child I was reading a lot of magazines and the end result was that I was sure I was a very bad mother. Nowadays with all these Instagrams it must be even worse. Everyone else has these beautiful and peaceful children, only me... And it is kind of expected that you will feel so happy about finally having your child. The reality - that there is no sleep, you are unsure of everything, you are afraid of doing everything wrong etc, plus the hormones - it sometimes really is too much. So even if you think she is overreacting, try to support her, especially with different chores. Tell her that she is doing much better than you expected from reading on the internet
Some other compliments should help too, but they must be sincere.
And I especially remember that we went to the doctor and he said something about the child having "too high tonus" (do not know how to translate it to English). I was really afraid etc. Later I talked with several people and it turned out that the majority of infants have it. It helps to know that even if it IS a problem, that it is a very COMMON problem.
And with the second child you just know - "Oh it is this thing they usually have about this age" and are much more relaxed yourselves and it makes a child less nervous too.