Isla Fisher is having a hot girl summer! According to an insider, the actress, 48, has been the life of the party since her divorce from ex Sacha Baron Cohen, 52. “He was controlling, so she’s really letting lose and celebrating being single again,” the insider said. “And pals are cheering her on, saying it’s the least she deserves following years of tension and unhappiness. It’s the first summer in a long time she’s felt truly carefree and happy. She’d never call it a divorce party, but that’s pretty much what it is,” they added of the redheaded bombshell. The duo announced they had split in …