Susan says she's been an attending for seven years, which is two more than Carter. However, Carter didn't become an attending until season 10- one or two years ago. Five years before this episode he was still a resident, not an attending.
The entire portrayal of the tenure process is wrong. For example, one is not "invited" to apply for tenure. Upon hire as a tenure-track professor, the norm is seven years to meet tenure criteria. If not, the professor is given a "terminal contract" after which they will no longer be employed by the university. Therefore, Susan's complaint that she was "not invited" to apply for tenure is completely wrong as is Carter's surprise tenure, if he had not applied for it yet. Despite his generous donation, universities have very strict rule that must be followed in the tenure process to avoid lawsuits from favoritism.