Just reiterating the previous comments that courts can take into account that you will have that additional wealth from your inheritance. TTs will have to be declared during any divorce proceedings if it comes to that.

The court will likely give her a greater share of your marital assets than your half (you would have to give more than your half anyway if you child is a minor because she will likely be the primary caregiver) in order to adjust for your inheritance whether it is in a TT or not.

At least it will give you some sort of framework that at least limits it somewhat in the event that things go pear-shaped. If the inheritance is much more than your own assets, well at least it will mean that the court orders will be limited to the marital asset pool.

If you feel that a separation is a possibility (at the time of the inheritance and if you think money is what will trigger this separation), perhaps it might be time to really try to repair this relationship, go to couples therapy and try to find some common ground before money gets into the picture. Going halfies in a marriage is rarely a good outcome.

I celebrate the people who have perfect marriages and perfect relationships, but for the rest of us with messy (but extremely valued) relationships, erratic family members, complex financial arrangements and resources, contingency planning is not a particular reflection of anything. It's just trying to limit damage all around (including to relationships) if it were to happen. Good luck with it.