From my experience (my son just turned 2), most kids eventually go back to their "normal" sleep pattern, & that there can be a multitude of reasons as to what interrupts their sleep. Rarely do I hear of a kid who never had sleep issues. Most kids have bouts of waking up at night - it's just a part of the process of growing. Yes, it could be teething, they could have an upset stomach from something they ate that day, something like a car starting at night could be waking her, she's remembering an event from the day that wakes her up, anything really.
And you're dead on - if you start a "habit" that is helping her get back to sleep, she'll wake for that too! Whenever our little guy starts to knock out of his routine, I make a very real effort to a)not spend a lot of time in the room with him & b) to make sure it's both mom & dad making sure things are alright. As long as there's no fever or any real sign of discomfort, I assume he's just waking for a reason I can't possibly fix & treat it as such. A quick hug, kiss on the forehead, tuck the blanket & walk out the door. If there's really something wrong, he lets us know it, but otherwise, he usually figures out that we're not spending all night with him in the room. We have made that mistake way too many times in the past & that can be a very difficult thing to break.
I wouldn't be so concerned about the "why" of it all unless there's fear, pain, fever, etc. associated when you go into the room. Just be loving, quick & consistent. She's still very young & will definitely be back to a more normal sleep pattern in no time! I, too, highly recommend the Healthy Sleep Habits book - it was a lifesaver for me!!