Alex, she has decided, cannot sing. At all. Like, seriously, you'd think a man who listened to music at all hours of the day would be a little better at it, but he's not.
Not that she can either, really, unless it was MMC marching cadence or the MCR anthem, both of which were skills he'd somehow managed to lose since his discharge. He'd managed to lose all sense of rhythm, and approached music like he did everything else -- by flow and feel.
So she smiles, laughs, and tosses a "Sounding good, cowboy!" his way and smiles as he laughs.