Bear in mind that the Marvel Cinematic Universe is one where a single man can design a revolutionary new type of weapon system in a cave! With a box of scraps! - while a team of normal researchers with top-of-the-line equipment can't replicate his work. It's possible that Maya is a similar genius, and that without her the Extremis project would stall.
It's also possible that she simply has an inflated sense of her own importance - her field is magical biology, not project management.
It's important to note that she threatens to commit suicide by Extremis overdose, while in the same room as Tony and Killian. Killian himself might have survived the explosion, but Tony - who Killian thought was vital to perfecting Extremis - wouldn't have. Maya was not threatening to kill just herself, but Tony and possibly Killian too.