Two things come immediately to mind: she isn't growing as rapidly as she was, so she simply doesn't need as much sleep as she did before, or; she is teething molars or has tooth decay that is distracting her from sleeping. Often the only symptom of dental pain is night-waking that is out of the ordinary for the child.
The other possibility that comes to mind is based on sleep-centre research: she's probably always been waking up that much, just didn't get you involved in it until she figured out that she could leave her room.
Sleep patterns of all (undrugged) people go from light sleep to deep sleep and back to light sleep in 30 - 50 minute cycles. Whenever people come mostly awake, they scan their environments to see if there is anything they need (and relief from irritating dental pain may be enough) they wake up fully and seek a solution. If they have no pressing needs, they fall back into a deeper sleep without any awareness that they were ever even slightly awake.
If she's asking for food, it's because she's waking up hungry. If she's asking for something to drink, it's because she's waking up thirsty. If she's looking for your attention, she may be waking up lonely or afraid she's alone (a very deep fear in all people, at any age). The shortest way to deal with it is to meet the need, and she'll go back to sleep.
You may like to lengthen (rather than shorten) or add another period to her daytime nap, as it is insufficient daytime rest periods that interfere with quality of sleep, not too much daytime rest, particularly in growing children.