Could be. Could be getting less lights than the others, could have been shocked for some reason and stunted a little while the others didnt. I have two of the exact same strain, germinated the same day, in the same medium, same lights, on the same watering schedule. when they went into flower, six weeks ago, they were the same size... now one of them is about 6 inches taller, and its buds took longer to fill out than the shorter one. could have just been a stronger seed, and a stronger plant just by genetics. my brother and I have the same parents...who raised us the same....he is taller than me, but I am stronger than him(don't tell him i said that)....shit happens in nature. Id just keep taking care of her, and she will grow and give you what you need.