The star played troubled Amanda Bynes' older sister in the series, which ran from 2002 to 2006, and when it ended, she thought her career was over.
And bit parts on the 90210 revamp and other shows didn't convince her otherwise.
It took Tv courtroom drama The Eleventh Victim, which debuted in America this weekend (04Nov12), to give Garth the spark to get back her passion for acting.
She tells Tv host Jeff Probst, "I forgot that I actually like what I do... I did the sitcom and I loved doing it... and then I went and did this dramatic role.
"I thought that I was done as an actress; I thought I was retiring and I didn't wanna do it anymore after my sitcom... (I was like) 'I don't wanna do this anymore...' and now I'm doing it and I actually really enjoy it."