I have a friend who is the daughter of a reform gioret (convertess) of conscience. She is very into Judaism. However, we know that, typically at least, a reform conversion process is not valid according to halacha. However, if such a person were to wish to become a full ba'alat teshuva, would s/he be able to be considered Jewish?
There is room to discuss the validity of most aspects of a Reform conversion - if the Mikvah was a kosher Mikvah, then that would be fine. If the person had in mind to be responsible and accountable for mitzvos, even if they did not intend to keep them, then it would be a matter of dispute if that is valid, but it is possible. The main problem is the attending Rabbis who are "performing" the conversion. The halacha is that גר צריך שלשה כמשפט - a convert needs a court of 3 eligible "overseers," as judgment does (Kiddushin 62b). Whether this is necessary for the point of acceptance of Mitzvos or for the Mikvah immersion, it is definitively required at some point. As your standard reform Rabbi is a public Sabbath desecrator, they are not valid even as witnesses, let alone as a standard of "Judges." Therefore, the conversion itself was flawed, and nothing done later can fix that original conversion which lacked a basic requirement. There is, however, no reason that it could not be repeated now that she wishes to do it correctly.
A Reform conversion is not considered valid, certainly not by Orthodox Jews, and in most cases not even by Conservative Judaism. (I saw Conservative Judaism, rather than Conservative Jews, since Conservative-affiliated Jews in many cases may have a more Reform view of halacha.) So to be considered Jewish by the general Jewish community, Orthodox conversion would be required.
Keep in mind that a convert is not required to advertise the fact that he or she is a convert (though the matter should not be concealed if it is relevant, as in relationships with kohanim). So if someone is raised Jewish, later realizes they are not halachically Jewish and converts Orthodox, it is possible that the person could refer to (or think of) themselves as a ba'al teshuvah, rather than, or in addition to, being a ger (since in some sense s/he is both.) I mention this not because there is anything wrong with being a convert -- far from it -- but only because you mention the term ba'alat teshuvah.