what is ironic about Zeena's ability to care for the injured Mattie and Ethan

Originally she was the one who needed the care.  Once they are injured, she essentially has to become the one with the caring skills.

It was ironic because before she was the one who was needing care and now she is caring for herself and others. She was never really sick. She just needed sympathy. She got it before through being "sick" all the time. But now she gets sympathy because she has to care for Ethan and Maddie. And now maddie the one who used to counteract the gloominess felt by zeenas "sicknesses" is the one bringing gloom