"The show has been on for a hundred years, and they have come at me a few times," the former Mork & Mindy star tells EW of her guest-starring role starting Tuesday night. "Either I just didn't want to do it or I didn't appreciate what it was they wanted me to do. Or it was near Christmas and it was like, 'I can't do this. I've got my parents coming into town.' I just haven't been interested in, you know, chasing the business. At this age, that's what you do. You'd have to really want it. I just don't want to put myself out anymore. You know the old song, 'I haven't got time for the pain. 'Then I guess they had created this character Marcie. Mark didn't tell me about it. Suddenly I have an email from my agent and I was like, 'Oh, poor Harry, my poor agent, here we go again. I'm going to turn him down.' And he goes, 'Well, you might want to read this.' I guess they were running names for who they could bring in for it and Mark said, 'You should be talking to my wife about this character.' The character is so good. I just fell in love with what they wrote. And then I had anxiety like, 'Oh my God, am I going to do this?'" Dawber also admitted that she doesn't like see herself on-screen. "Well, how everybody has a large-screen HDTV," she says. "I can't say I was ever delighted when I saw my episodes with Robin Williams, you know, how many years ago? All of the fear bubbles to come up. Can I even remember lines anymore? What if I suck?"