As far as plant care for orchids it sounds like you know what you are doing and have made no errors so I would first closely examine the orchid for pests such as scale, mealybug, ants, as well as fungus. Ruling that out check for drafts around the bathroom window which could cause sudden temperature drops during the times where the wind blows against the window which indicates insulation is breaking down. Finally, if all the above is ruled out and the situation of leaf death continues, perhaps it’s time for a new orchid.

On the other hand no individual leaves go on for ever.
She might grow some new ones when the season has progressed a bit further. Fingers crossed!

Phalaenopsis, Paphiopedalum, and Vanda leaves can last 2-3 years, each, but most other types of orchid rarely keep any particular leaf more than a year.