Recommendation: The Heather Wells Mystery Series by Meg Cabot

Size 12 is Not Fat: When you peak at fifteen, where can things go but downhill?
Former teen pop sensation Heather Wells has hit rock bottom: tired of singing other people’s lyrics, she hasn't exactly been bombarded with recording contracts for her own songs. Worse, Dad’s in jail, Mom’s bolted for Buenos Aires, and Heather can’t seem to stop drowning her sorrows in Kit Kat bars. To top it all, Heather's fiancé Jordan Cartwright has replaced her – on the charts as well as in his bed - with America’s newest number one pop sensation, Tania Trace.
When Heather finds a job in a New York college dorm--right around the corner from her temporary digs in her gorgeous friend Cooper's attic apartment - things seem to start looking up.... at least until girls in the dorm begin to perish at an alarming rate. Elevator surfing is the official explanation from university administration, but Heather has other suspicions, and - enlisting a reluctant Cooper's aid - she attempts to get to the bottom of the rash of teen deaths in the building where she works, never knowing that it isn’t her supper she’ll be singing for this time, but quite possibly her life.

Size 14 is Not Fat Either: It's the first day of the winter semester at New York College, and assistant dorm director Heather Wells has a lot more to worry about than roommate conflicts. One of the New York College cheerleaders has lost her head - literally - in the Fischer Hall cafeteria, and no one can find the rest of her.
With the entire population of the dorm under suspicion for murder, it doesn’t look like anyone on campus, least of all Heather, who is starting night classes, is going to have a good semester. She’s got a decapitated cheerleader and a demoralized student body to deal with, as well as enough guy problems to make a normal girl seek shelter in a convent. With her ex insisting she has to be at his wedding - The Celebrity Wedding of the Decade, her incompetent new boss freaking out over his job demands, her long lost father looking to reunite (with an eye on Heather’s far-from ample bank account), and the love of her life still no closer to realizing she’s the girl of his dreams, it’s no wonder Heather prefers questioning suspects to dealing with her personal life.
But when the murder trail leads her to the door of one of New York College’s oldest and wealthiest fraternities, Heather finds that initiation rites have been taken to a whole new level . . .

Size Doesn’t Matter: Heather should be happy. She’s finally got a boyfriend and although he was only supposed to be her "rebound guy", things have gotten serious fast . . .
She's also actually passing her first college course, and better yet her dad’s moving out.
On the down side, her boss, Dr. Veatch, may well be the most boring man on the face of the planet . . . But that hardly seems reason enough to put a bullet through his head. Can Heather find her boss’s murderer, answer Tad’s question, and get her landlord Cooper to realize that by letting her go, he’s making the biggest mistake of his life, all while maintaining a fifteen hundred calorie per day diet?