Rose woke suddenly, suppressing a scream. She blinked in the early morning light, trying to reconcile her familiar bedroom with the nightmare. Rose had wakened this way almost every morning for the last two years. Beside her, she could hear an unpleasant snicker from her older sister, Emerald. Emerald enjoyed tormenting Rose with nightmares. It was no use complaining to their mother. She always took Emerald’s side in everything.

“You should find a better use for the gift, Emerald,” Rose said.

“What could be better than watching you try not to scream? I find it very entertaining. Almost as entertaining as when you do scream.”

I think the execution could use a little bit of work, though. I'd give you a few more lines based on the concept of a mean, dreamwalking sister, but you'd really have to wow me with what came next to keep me going.

The MC waking up to start the story has been done to death, and isn't often done well. Here you drop an adverb in your very first clause, modifying the dull verb of "woke" with "suddenly", which is the worst adverb in fiction. I think you're trying to establish tension here, but in the next sentence Rose seems comfortable, so I'm not sure what I'm supposed to feel.

Then you tell us this happens all the time (using the same verb "wakened" again), which kind of explains the change in mood, but then wouldn't irritation be the better reaction than terror in the first sentence? Also, it isn't clear to me why their mother would take Emerald's side. Sure it seems that way to young children (though the dialog leads me to believe they would be mid teens, at least), but in the case of one child literally tormenting the other on a regular basis I'd expect something more. Does their mother not believe Rose (that the gift even exists or that Emerald uses it to torment Rose)? Does she think Emerald should practice using it, so Rose should learn to handle the nightmares? What's going on in this household?

A few nits - "she could hear" should be "she heard". Also, think about Rose calling it "your gift" when speaking to Emerald, rather than just "the gift", unless the power is commonplace or Rose has it, too. Finally, you might want to cut out some adjectives early on. For example, snicker is great verb (and the right one to use there) that will be interpreted as unpleasant or snide without any adjectives at all. "Unpleasant snicker" coming close on the heels of "familiar bedroom" (whose bedroom isn't familiar to them?), which itself follows "early morning light" (that one didn't bother me at all), makes me wonder if I'm diving into an adjective-fest... then there aren't any for the rest of the passage.

I would strongly recommend starting the story a little later in the day (breakfast table, maybe?), but with the action still being a confrontation between the sisters.

I admit, I had to suppress a groan when I read the first couple lines. My gut reaction was, "oh boy, _another_ story where the MC wakes up from a dream/ nightmare/ sleep."