You are her partner.
It is not your job to tell her how to feel, or to determine by yourself the best plan for your future, and then "rationally" explain it to her.
It is your job to support her as an equal, and a partner.
"Talking her off the ledge" is a warped way to put what appears to me to be substituting your wants (her to keep working so you can retire early) for hers (raising the child).
Definitely communicate. All the time, non-stop.
But that doesn't mean you just explaining things to her. It means listening, and problem solving together.
Throughout this thread your responses have all been why you need to get her back to work, and how you can do that.
I would suggest that your whole approach to this is not conductive to a healthy relationship.
There are more important things then FIRE. If you to decide together
that the best thing is for her to keep working, okay. But you going into that conversation with the goal of convincing her of that is not fair to her (or your relationship, or possibly your child).
Don't misinterpret me: I'm not saying I think she should stay home. I don't know nearly enough to have a thought on that.
What I'm saying is that your deciding on your own that she should go back, that her wanting to stay is just "emotional" whereas you are being "rational," that you have to "talk her off a ledge," etc. is all quite (many terms could go here.. arrogant, selfish, egotistical, short-sighted, disrespectful, etc.). It's the wrong way to approach the situation.
I don't think you're a bad person, I just don't think you're considering what your wife wants... you are just thinking about how to convince her off what YOU want.
As evidenced by your questions here. Not asking other moms how they've felt in similar circumstances to understand your wife better, but asking how you can convince her.
I know my post will raise immediate hackles/defenses.
You don't need to respond, or defend yourself. I'm just a stranger on the internet. Better not to reply to me.
But I hope you pause your immediate reaction, take a break, and revisit some of these ideas, maybe in a few days. Think: How can you support your wife?
That's the goal, much more than quickest FIRE.
I brought up the possibility of extending her leave by a month, unpaid, to make the transition slightly easier. She immediately thought this was a great idea. We also talked about how her boss is okay with her working from home 2 days a week, and if she crams all of her work into the 3 days she has to work at the office then it can almost be like she is working part time which is pretty ideal.
This is great! Nice that her company is so supportive.
Might be a good way to help work something you both are happy with.