My sister was suffring from aml m2 & now after one year in blood test platelets gone down to 16000 & lymphosytes are 86% & atypical lyphocytes ++?

Concerning... Of course, given the history of m2 aml. AML therapy can have a significant effect on marrow reserve, rendering patients susceptible to suppression from infection, for example. In this case, the presence of atypical lymphs could suggest a recent viral syndrome with associated thrombocytopenia. However, to not consider the possibility of disease recurrence would just be wrong. She needs to see dr.!
Concerning... Given that you know these numbers (low platelets and increased lymphocytes with atypical lymphocytes), I assume a physician is following these numbers. A pathologist can look at the atypical lymphocytes and special tests can be performed if there is a concern of relapse. A viral infection could also cause these numbers, as long as the atypical cells are confirmed not to be blasts.