Child custody laws in Bucks County, PA?

If a mother dropped her child off to a grandparent & didn't return for approximately 2 years, is this considered abandonment in Bucks County PA? If so, would she be able to regain custody, and how hard would it be for the mom? I'm asking because someone told me about this happening but there seem to be holes in their story, and I'm curious about the legal side of this "story". Thanks.