B’’H SHalom, I am a Shabbat Observant Jew, so naturally I don’t recognize so-called female "rabbis". But, I am wondering, why can’t females become rabbis? I heard that it has something to do w/ them not being qualified to be witnesses? Is this true? What are the sources for this? And any and all information you can give me on this would be greatly appreciated.

This question is more than a bit complicated. Today, certain functions that were rabbinical in nature are performed by women. There are woman Torah teachers, halachic advisors, spiritual guides. Some rabbinic functions, such as running the services, would be unthinkable for a woman in an orthodox setting. I do not know of a program that brings women to the level of talmudic and halachic expertise that a rabbi requires. I do know individual women who are fantastically learned and could be consulted on halachic matters. I am unaware if there is a woman with such expertise on the highest levels of scholarship, but I do not find it inconceivable.