What are the symptoms for mercury poisoning in children? Are they any different from adults?

Let me give you a little information about my daughter . . . . . .
We adopted her from China when she was 16-months old. She was in an orphanage prior to us adopting her. At that time, she was very malnuourished. She weighed only 16 pounds, couldn't crawl, couldn't walk, & could only say a couple words. Needless to say, we had our hands full to get her up-to-date.

Now at 9 1/2-years-old she is very healthy. She is still tiny - weighs about 45 pounds & is about 47-inches tall. But she is never sick.

On the other hand, she has some symptoms that I can't figure out what is going on. She had physicals, blood works, etc & nothing shows up. At this point, she down right refuses any more blood tests - she is very fearful of needles & such.

Her symptoms include:

Always hungry - never feels full
Anixiety (always rushes to get things done)
Bloated Tummy
Cries for no reason at all
Doesn't listen
Forgetfulness
Low Blood Sugar
Sensitive
Smaller than peers
Tires easily

She has no fillings in her mouth whatsoever. Her symptoms started prior to vaccinations.

Could this be mercury poisoning? If so how & where did she get it?

Thanks!