Faye is usually very serious, calm and collected. She's very reliable and a workaholic. It's her goal to keep everyone else safe, and she does her best to help others out.
A reason for her working so hard is because she wants to compensate for her poor judgement of situations or when it comes to judge people.
Her poor judgement might get her into trouble or make things worse than they used to be. So she does her best by simply working as hard as possible, as well as concentrating on the things she's good in (Her poor judgement doesn't concern her healing abilities, it's mainly when it comes down to tactical decisions or when judging enemies or allies etc).