O'Brien originally tested for two other roles on DAYS. She said:
I went in three times and screen-tested with Greg Vaughan [Eric], but I wasn’t right for that. They just envisioned somebody different. A year later my agent called and said, ‘Will you go in and read for this other role?’ I remember going in and it was very ominous in the room. [Casting Director] Marnie Saitta and [Co-Executive Producer] Albert Alarr said, ‘Well, we’ve got good news and bad news. The bad news is that you’re not going to be playing this role, but there’s a new role that we want to mold around you.’ That’s when the character of Gwen was born. She’s British. She’s wonderfully unpredictable and volatile and she’s completely fearless. She lives on the edge and with complete passion.
I feel very lucky. Olivia is young. I didn’t realize how young, but she was so ready for anything. I just was playing and she would play back, which was so nice. It was really refreshing. And the thing with Brandon…. I got very lucky to be paired up with him. He’s ready for anything, ready to go on, loves to rehearse. He’s so incredibly prepared. When we go up [on set] it’s like a ping-pong game. I’ll throw something at him. He throws something back. That just keeps it really fresh.
And she's slipped right back into rapid-fire soap pacing. She noted:
It was so weird. I was incredibly nervous [when I started on the show] because I had been used to these long, long, drawn-out rehearsals with video games and movies that you shoot for a month. I had heard that DAYS moved even quicker than Y&R does. My heart was pounding. I remember I had to do two episodes in one day, and I just had no idea how I was going to do it. I think I blacked out on my first day. I don’t remember a minute of it. But, you know, you get back out there and you kind of go, ‘Okay. It’s the same thing.’ You get on the bike, you remember what it feels like, you get that adrenaline rush again, and it’s just, go. DAYS does move a bit quicker than THE YOUNG AND THE RESTLESS, but it keeps you on your toes. It keeps everything really fresh.