The fact that she wants to do it in her ovulation period maybe it’s not only to increase the possibilities of a pregnancy but also because naturally her libido is higher.
But, of course, I understand that you feel pressed and the more stress you feel, the worse in this case.

She should understand that. Did you, guys, contemplate the possibility to see a sexologist?

It seems as a one of the most natural thing and the easiest activity to do but sex can be affected by many circumstances because it sparks in the mind and all of us know how complicated mind may be.