Your grammar is absolutely terrible, it was pretty hard to read just for that reason. Commas impose a pause in the thought, a pause in the tongue when the character is thinking or speaking. So instead of the character spewing what sounds like a mindless, childish sentence like "I mumbled under my breath walking over to the door I cracked it open," That sounds like toddler babble.. There should be pauses, some emphasis, if you will. "I mumbled under my breath. Walking over to the door, I cracked it open." You see? The actions are separated, making the scene more collected, maybe even more chilling?
Also, your character is not likable, is not relate able, and has no just motivation. Why would anyone want to read about a character like that? I love villians, but your character has nothing in her to keep a reader interested. She's not even a "villian," she's just a psychopathic killer. Even psychopathic killers get boring if there is no depth to them.
/Opinion.