Fear of loss drives people to behavior that it they would not exhibit otherwise. The fear of isolation is probably one of the largest human fears. I can empathize with the person you describe, but like you i question her wisdom.
All of us who transition with a spouse have to understand there is a risk of driving a wedge in the marriage that is unsurmountable. I read in the recent study about 50% of young married folks divorce over it, and perhaps 60-70% of older married folks do (i would have thought it should be flipped, but that is what it said)
When i told my wife i wanted to transition and begin HRT, we had a lot of work to do (despite the fact she always knew me as a feminine guy) and that work is ongoing. We both are committed though and i would say we are now closer than we were in the past. She would agree.
I'm guilty of keeping things from her, I've not been a princess/prince of good behavior at times, but i've learned as we have aged, that trust is more important than avoidance of conflict. I've also learned that very important fact that not all disagreement will be resolved. Sometimes you have to agree to disagree and move on.
One could question marriages that are fragile enough that fundamental fears and struggles cannot be expressed between spouses. But i feel a little moralist in doing so, because i know that we are all imperfect beings that attempt to pair up for life, and we get all the good and bad that goes with that.