IS MY TODDLER UNDERWEIGHT?

She's turning on 22 months old this coming july 19 and when i checked her weight she's only 19 lbs. Well, first of all, let me say that she was born premature at nearly 36 weeks and plus she's fed (tho she drinks a lil of soy, cow's milk and pediasure, which isn't even really a cup per day, and the rest are milk). My body structure is small, 5'2'' and 100 lbs. and her father is not that big of a guy either. She eats about 4 small meals in a day and twice of little snacks. She's very energetic, just everywhere. Since from the time she was born, she only got sick twice, first, when she had 3 successive shots and they drew out blood from her for lead testing in her blood, in one day. She cried a real lot that time, which I guess gave her a slight fever during the evening. And, the next day, she's back to her well-being. The second time she got sick was when she fell of the chair, bit her lips accidentally which resulted to a canker. That, she had a fever for about 5 days and the canker stayed for quiet a bit more days. Just yesterday, I weighed her and she's 19 lbs. The last time we went for her well-visit (she was 18 months old), she was 18.5. Is she undernourished? I mean, when it comes to eating, she eats vegetables, fruits, whole-grains, dairies, certain beans and beef, and yah, shrimp as well (her all time favorite). She doesn't eat eggs at all and for the chicken, she'll only eat it if it's sweet and sour.