“Musical teeth?” What on Earth does she mean?

I just received this rather baffling pair of sentences in correspondence:

Tenors are usually like hens' teeth and about as musical. We think your teeth are more musical than that!

The context is that I regrettably had to call in my absence due to having taken ill. I think it is meant in a positive sense, but I can't make heads or tails of it.

Expanding upon Dan Bron's comment:

Hen's teeth is an idiom meaning either vanishingly rare or nonexistent (because birds don't have teeth).

She's saying it's hard to find tenors, and even harder to find ones with (musical) talent. Because you are tenor with musical talent, she regrets your absence, and wants you back for the next performance or practice or whatever.

See: Scarce as hen's teeth — Dictionary.com

"On a rainy night, taxis are as scarce as hen's teeth."