[Edit: Corrected to assume that you both are over age 55, not under.]
Since your wife was covered by a family plan on April 1, she can make a contribution for April based on the contribution limit for having family coverage. Assuming that you made regular contributions to your HSA of $1,775 (plus $333.33 catch-up), her regular contribution for April is $591.67 and for each of the months after that is $295.83 . Assuming that she remains eligible for the remainder of the year, her total contribution would be $2,958.33 (plus $1,000 of catch-up if she too was age 55 or over in 2020).
