Does this sound like a simile or irony or both?

Question

She is the only lady I have ever known who was as charming when she was drunk as when she was sober

Answer 1

I think what you've got there is a back-handed compliment.

Answer 2

Edit: It's neither. Not a comparison using like or as or an incongruity between what is spoken and what is actually so.

Answer 3

Simile, I believe.  

Answer 4

It's neither.

If it had said, "even drunk, she acted as sober as a Mormon", that would be a simile.

And it's not ironic that someone is charming whether they are sober or not.