The star admits she was desperate to try out a new role and jumped at the chance to portray actress Elizabeth McGovern's lesbian lover, Jane, in the emotional movie, which also features Jeremy Piven, Thomas Dekker and Mira Sorvino.
Walsh had to stick to a strict travelling schedule to make it all work as she was shooting Angels Crest and her hospital drama simultaneously, but she insists it was the best experience.
She tells WENN, "I was so thrilled to be let out of my television show to finally do something other than (Private Practice character) Addison. I was on cloud nine and I had such a great time.
"I flew back and forth (between sets) about 30 times. It was a delicious part for me to play. I didn't want it to end."