I think considering having a frank talk with her is the only way to find a solution or at the very least gain more understanding.

Do you feel she has been avoiding sex? If so, perhaps that's something to bring up. Or you could simply say something like

" I noticed things have been relatively calm recently, yet our sex life is the same as when things were more stressful, if you dislike sex, or perhaps dislike sex with me, or if it's something else other than what you've told me, please let me know.."

And are you considering leaving over this issue?

Anyways that's how I would go about it, you can change it to how you would do it, if you consider this course of action. The possible downside is that she could take offense to you doubting what she usually says. I don't know, only you do.

But if having a frank discussion is something you've already done, or won't consider doing. Then I suppose, what are you think regarding this issue at the moment? If anything has changed.