Happened to me last fall. Eustachian tubes swell shut. You are deaf as a doornail. I ordered a product from Amazon called Eustachi. It helps force air into your Eustachian tubes to open them. Also, she can hold her nose and blow like you would to adjust your pressure on a plane. Give it about 6 weeks.
I lost my hearing in my right ear back in the fall of 1988. Pretty much one minute I had it and the next minute I didn’t. Felt dizzy, sat down and rested a bit (was on a field project in Arkansas at the time) and got up feeling fine except for hearing loss. It was strange at first.
The usual round on family doctor, two audiologists, the verdict was no hearing in the right ear but the ‘good news’ was that there was no instance of the second ear going like the first in the literature at that time.
They advised not to try the hearing aids available then, they just didn’t work. After this long it really doesn’t matter all that much to me, I’ve just got used to it.