Desperate for help with a vanda

[GhostPrincess]

I bought a blue vanda orchid for my grandmother a few months ago and it was doing very well but suddenly it started to die. It's flowers and all of its leaves have fallen off over a period of about a month and I'm very worried that it isn't going to make it.

I water the orchid twice a week for thirty minutes once on Monday and once on Friday. It is kept in two places a south facing room with large windows protected by a larger ficus tree. And in a dining room that recives light from the same south facing windows but is more shaded. I used a water soluble fertilizer when watering it today (Friday September 1). I would like to know what else I can do to help the orchid come back or if it's a lost cause.