Thanks for posting on HCM
According to the manufacturers of the product you can experience various side effects including crampy abdominal pains ( sharp) and heavy or continuous vaginal bleeding. So it is possible that she is suffering from two of the side effect of the mirena
. Another possibility that will require that she sees an obsgyn immediately is the fact that she could be experiencing an ectopic pregnancy
(more specifically tubal pregnancy) which occurred as a secondary effect of the presence of the mirena.
I strongly suggest that you meet up with your gynobs for proper review and management of your step sister's condition.
Wish her the best.