Agnes Flanders was a beatnik, revealed when a much younger Agnes and her husband were seen bringing Ned to Dr. Foster.[1] Ned reveals that Todd and Rodhas at least one living grandmother, Agnes is still alive due to attending Ned and Edna's wedding. Although Ned Flanders is willing to help Agnes Flanders, he secretly hates her as well as his father, which he admitted when various Psychiatrists attempted to trap him in a room with Homer to get Ned to admit to any kind of anger he may have felt that led to him suppressing it due to Dr. Foster's treatment backfiring.
Flanders once said, "Homer, you met my parents" (to which Homer replied, "Not naked I haven't", as he was naked at the time), so they are probably alive.[2] In the latest season, it is shown that she and her husband is alive, since they both attended Ned and Edna's wedding.
It is likely that Grandma Flanders is actually Ned's grandmother, since the Flanders family tree in Flanders' Book of Faith is exactly canonical to the series.