The adjective morose means someone who is miserable, bad-tempered, and not willing to talk very much to other people.
Synonyms are cranky, depressed, pessimistic, or gloomy.
The word origins from Latin morosus meaning “morose, peevish, hypercritical, fastidious”, and mos meaning “habit, custom”.
I guess she must be a bit morose about it.
Molly looks rather morose but I still continued explaining my argument.
Sarah became morose after she lost her job.