I used to believe Nepal was a tolerant place, those were good old ignorant days of me. This incident has become like the Bollywood actor incident. I won't be surprised if few will take it to the street.
If such small incident is a pain in the butt, what will happen if few Nepali Muslim jihadists make it to the international news. Those days will come soon in the future.
She has the right to deny to sing any song she wants to. Unless you are so unsecured about your existence of your religion or a hard liner, I don't see any issue with it.
What next? She refused to celebrate Dashain?