How about, "I think you should sing solo -- so low no one can hear you!"
For the male who can't, there's, "I think you should sing tenor -- ten or twenty miles away!"
(It occurs to me that your chosen screen name is a bit musical so maybe those are old jokes to you. If so, sorry!)
More seriously, if she's doing it while people are trying to get work done, a talk with the boss about distracting behavior might help.
@billblake2018 I can't sing worth a damn. It's the thing that's always held me back in music, due to the difficulty finding reliable singers. :(
@AriaDiMezzo I mostly sang for social reasons, and wasn't driven to it. I got good enough to be occasionally asked to sing, but not much better. Then life happened and singing was just not on the agenda.
@billblake2018 I sang in three of mine, but only because they were really good songs that I didn't want overlooked because "But there's no singing!"
@AriaDiMezzo That's one of the sillier prejudices about music. Fortunately, I grew up with classical music so I know better. :)
One of my bigger beefs about some pop is that there'll be this instrumental intro and I'm like--this is a whole damned symphony if only you'd let it go! But of course, there have to be lyrics and in just a few seconds....
What style of music do you do? (I'm short on bandwidth or I'd download and listen.)
Liberdon is a Mastodon instance for libertarians, ancaps, anarchists, voluntaryists, agorists, etc to sound off without fear of reprisal from jack or zuck. It was created in the wake of the Great Twitter Cullings of 2018, when a number of prominent libertarian accounts were suspended or banned.