If halacha on an issue is firm and no posek anywhere says it’s muter when asked, then there’s no heter. It’s not like the shaila of birth control where a heter may exist depending on the circumstances. “Silence” by a Rav where he sees that you’re not going to follow anyhow, is not a heter.
The reason I’m being adamant on this issue is that years ago I was seeking a heter on this very issue for a relative and was advised to go to various Rabbonim who “for sure” would give a heter. One person even gave me the name of a well known Rav whose daughter was divorced and she did not cover her hair. I checked it out with all the Rabbonim and guess what, NO HETER.