Welcome to HCM,
There are many causes of spleen
enlargement,her CBC and Mono test are normal,so do not worry but as there is family history of AML,just wait and watch and keep her under medical supervision.
can be repeated and if Hematologist
thinks it is appropriate a bone marrow examination
can be done.
One should be positive ,I hope spleenomegaly will regress or other cause if any will be detected and treated and she should be better soon.
Best of luck