Cheryl Fleming is the mother of Sharona and Gail Fleming. When her husband, Douglas, died, she was left to raise two kids alone. She visited Sharona in 2003 when Gail was framed for murder.
She begged Monk to take the case, which he eventually did, though reluctantly. She believes (as a result of a number of lies Sharona told her) that Monk and Sharona are partners, rather than Monk being the detective with Sharona as his assistant. Some time later, she ended up becoming very ill, with Sharona ending up having to visit her for a few weeks. It is possible that she died shortly afterwards.