no reason why not. Women often have strange tastes in colours. It will be good practice for when she has her own house.
Encourage her to wash down the walls first, apply plenty of dustsheets, wipe drips and spills off the paintwork before they dry, not to kick the paint over very often, do the edges first and fill in with a roller, apply several coats not one thick one; move the roller slowly to avoid excess splatter. Make sure she does her own prep and cleanup.
In time she may grow to love beige, taupe, and barley white.
You can easily paint over emulsion as long as it is not blobby, runny, or two thicj with brush marks.