The closet has worked, as has the garage.
For my daughter, she likes the sound we get when she stands in the upstairs hallway that faces the open stairwell to the downstairs, she says the stairwell sucks the room sound away, yet the side walls help her hear herself.
Ya never know what's going to work for a given vocalist, all you can do is experiment.
Heck in Motown they would record on the dirt floor of a garage and feed the sound into the empty attic for reverb.
Nothing wrong with being creative and experimenting.

/But I wouldn't initially invite her over to experiment, not in those words anyway

Make your sound your own!
.. I do not work here, but the benefits are still awesome