By Nancy Rugart Plummer, Columnist, The Times Dear Nancy, I was all ready to start dating again and even got a subscription to Match.com, when my mom called to let me know she has cancer. Now, she is in her 90’s and has many people, thank goodness, to take care of her, but I’m just feeling guilty. Am I wrong to want to go ahead with finding someone? – Maria, Age 70, Newtown Square Dear...