prunus (1yr old) needs help

I have a winter-flowering cherry that has a similar problem: it flowered intermittently through the winter, got lots of rain in the spring, but suddenly about 1/3 of the leaves died back.  It is weeded, fertilised and mulched.  I contacted the seller and sent them a photo.  They think it's probably frost damage - I suspect that it's actually a combination of frost and cold/dry north-east wind.

I'm hoping it recovers...