Not sure if she was a Timelord or not. From her advance knowledge she had had some form of education but it never stated if she reached the level of Time Lord. Of course River could without being a Time Lord but that was a different situation.
Alternate answer The series has never been totallly clear as to who can regenerate - whether it's a trait exclusive to Time Lords or available to all Gallifreyans, and also as to whether all Gallifreyans are Time Lords. The most firm indication we have that Gallifreyans are capable of regenerating as a species comes from "A Good Man Goes to War" in which River Song/Melody is explcitly said to have "Time Lord" DNA. One does not train DNA. And Melody/River regenerates at least twice ("Day of the Moon" and "Let's Kill Hitler") without being a "trained" Time Lord. The novels and audios have suggested that one has to be a trained Time Lord in order to regenerate, however. Susan, for her part, has never been explicitly defined as a Time Lord, but she has never not been, either (except in some literary stories that suggest she wasn't the Doctor's actual granddaughter).