When we first met Alex in Season 4 she was full of life. She didn't stay that way for long, though.
Fun and flirtation with Hal soon turned sour when she was killed by vampire Cutler in retribution for Hal killing his wife fifty years ago. Hal then did the one thing he'll never hear the end of from Alex: He drank her blood.
Marooned in the afterlife, Alex knows she's lucky to have two mates in Hal and Tom to face it with - she would just never tell them that. Having died so young, she's certainly got plenty of unfinished business to attend to.