Albert Barnes Commentary 2 Samuel 20:18

"Then she spake, saying, They were wont to speak in old time, saying, They shall surely ask [counsel] at Abel: and so they ended [the matter]." — 2 Samuel 20:18 (ASV)

This was an old proverb. Abel, like Teman and some other places, was once famous for the wisdom of its inhabitants (1 Kings 4:30–31). The wise woman was herself a remnant of this traditional wisdom.