L.M.
I say let her wrestle!
Since they are wrestling kids of similiar weight it isn't so bad. Keep in mind that boys hit puberty later which means that typically an 8th grade girl may be stronger than the boys (that will change around 10th grade). Girls tend to be better with "putting in legs" but should not try to out muscle...they really need to out wrestle very quickly. If you girl is not small and petite she will encounter a strength disadvantage in the upper weight classes as she advances. If she is about 125 lb or less (in high school) she should be able to do just fine.
Some boys won't want to wrestle her because if they win they "beat a girl", if they lose they "lost to a girl. It won't always be easy, she needs to know that.
My son wrestled so I have seen girls wrestle as young as 4 years and as heavy as 189 in high school. I don't have a problem with it (my husband does).
Both the boys and girls need to realize that when a girl steps on a mat she is not a "girl" she is a wrestler and her opponent has to wrestle her as such...no special treatment!