In most of the world, people are jailed after acting on split decision choices. An example is somebody who decided to overtake in their car and caused an accident which ended up in a fatality.
Whilst I'm not suggesting that any fatalities occurred in her case, she did however have plenty of time to decide on the course of action she was going to take. There was plenty of time for her to weigh up the pros and cons and therefore joined ISIS with her eyes open.
She is also mistaken when she says they are not all terrorists. She certainly never joined to promote peace and this is definitely a case of guilty by association.
She rejected Irish society and their values and now needs to face the consequences of her decision.