Derech,
I’m glad your wife in on such a high madreiga. I say, without any malice or sarcasm, that I’m happy for you and wish you both extreme happiness in it.
Nonetheless, not everyone is up to that, nor should everyone automatically be “pushed” up to the strictest level of observance on every issue. Some people just don’t want it (for whatever reason) and, since it’s not actually forbidden, it’s not your place to say that they are wrong. If a woman wants to keep her hair uncovered when she sleeps, showers or even when just home alone, it’s perfectly alright in halacha.
The Wolf