Real-life 'Mamma' glad to be home BY MISHA DAVENPORT
It happens every night at the same time. On stage, well into the second act of the hit musical comedy "Mamma Mia!," Dee Hoty--who plays single mom Donna in the show that opened Friday--moves tenderly through ABBA's "Slipping Through My Fingers."<br /> And Chicago actress Rosalyn Rahn Kerins--who plays one of Donna's best friends, Rosie--is backstage fighting back the tears. Some nights, the mother of a 17-year-old so…