Mother could be white or could be mixed race. That's her on the right, below. The name, Imelda, was given to a 14th-century Italian nun, indicating that her parents may have been well-educated; she and her husband raised their adopted son Seth as a Roman Catholic.
Philly.com: Seth Williams announcing his run for district attorney against Lynne Abraham in the 2005 Democratic primary. Also with him in photo are family members, from left: daughter Alyssia, 17; daughter Taylor, 5; wife, Sonitha (partially obscured) and at right, his mother, Imelda Williams.
This is a sad story if he was ill-intentioned in draining her account rather than just a sloppy bookkeeper of the estate; there may be more to the story. Seth Williams has been considered one of the good guys for being pro-life and supporting many pro-life organizations; importantly, Williams was the lead prosecutor of abortion butcher Kermit Gosnell.
Just looked up his home church, and while it appears to be majority black, it also looks very well-furnished and maintained, indicating solid parish support. Check the photos of the many nice-looking, well-dressed parishioners.