My snake hissed at me when I first got her. I just picked her up, and handled her anyways. I pretended she didnt scare me. She got over it real quick. Dont be nervous. She can tell. If she bites it wont hurt so just show her whos boss. lol Ive had my little girl just over a year and she is just now completely comfortable with me. (ie I can touch her head/kiss her and hold her neck)
As far as the health part goes, I dont know. There could be something hurting/bothering her that is making her act that way. Could be hungry, could have parasites, etc. Im sure other members will have more information about this!