5 feet tall and 90lbs?

That;s me when I am not pregnant. As long as she is eating a healthy balanced diet then she probably just has a small frame.

I have been 5 ft 2" since my freshmen year in high school. When I got pregnant at 19, I weighed 93 lbs. That was the most I ever weighed in high school. I ate well, I just didn't gain weight. Unless she is unhealthy looking (skin, hair, etc...) it's pretty much okay.

that sounds normal to me as well. 5' is not very tall at all....petite.

My sister was 75 lbs at five foot and my oldes son was about 85 lbs when he was that height.

I am 5ft tall and weighed 96lbs on average all through high school. I was too skinny in my opinion and yes it is considered underweight, but I just couldn't gain the weight no matter how hard I tried.

My daughter was that much at that height. Now she is 5 ft 8 in and about 130!

I was 5 ft 2 and 90 lbs for most of jr high. My highest weight as a teen was 115. I was not underweight.

I would say that's pretty normal. She'll probably gain a little bit during puberty and fill out a bit more.

i was 5'4 and 95 lbs when i was 18. some ppl are just naturally skinny. i been told my kids are underweight, they are younger than your niece but my 8 year son is 50lbs my 6 yr son is 40lbs and my 3.5 yr daughter is 27lbs. they eat non stop and mostly healthy foods and are also really active.
are her parents heavy or skinny? what about other family members or siblings? if she is skinnier than the norm in her family it may be a good idea to get her thyroid checked. they did all kinds of test on my middle and youngest child cause they are soo tiny, everything came back normal but then again my family is all tiny. underlying health issues may cause one to be under weight, but chances are she just has a high metabolism and nothing wrong with that.