I have another question. Since Rumia manipulates darkness, and darkness is the opposite of light, does that mean she has control over light to a certain degree? And vice versa with Sunny Milk?
Actually, I've thought of that for a while.
Rumia doesn't really ''control darkness'' in the proper sense of the term; The most she can do is create an orb of darkness in which you can't see much, or make it like a summer night.
THUS! in conclusion, Rumia's ability is like Cirno, that is not to create/control what their power specify, but rather creating an absence of the opposite (Light/Heat), as neither cold nor darkness physically exist.
...In more simple terms, Rumia is a light-eater. So, unless you count that as ''controlling light'', then no.
Also Sunny controls light's refraction, not light itself.