She's earned herself a great reputation, whether in the Broom Cupboard, sharing the screen with Otis The Aardvark or showing off her artistic side on SMart.
Now, though, she's at a crossroads.
As she explains in new BBC Three documentary Kirsten's Topless Ambition, fellow female presenters with much less experience are now way ahead.
Thanks to a couple of smart career choices, the likes of Fearne Cotton, Holly Willoughby, Angelica Bell and newcomer Caroline Flack present huge primetime shows on major channels, leaving 37-year-old Kirsten feeling left behind.
This month's FHM features ex-Blue Peter presenters Konnie Huq and Zoe Salmon on the cover - exposure which is likely to propel both of them on to bigger and better things.
Kirsten doesn't believe there's any conspiracy behind her career plateau, or that the other girls possess skills she doesn't.
She thinks it's because they've all appeared in saucy magazine shoots for lads magazines.
"I still have the GQ with Gail Porter on the front, and a Sky magazine with Cat Deeley on the cover," she explains.
"Over the years, it's something I've watched women do, and it's fascinated me.
"Now I'm at a career crossroads and that's the usual point in which women do a shoot, when they say 'I want to get out of kids telly, what do I do? I know, I'll get me swimsuit on and get me la las out'," she says, laughing raucously.
As Kirsten is keen to point out, the documentary is not an attack on lads magazines and the girls featured in them.
"I'm not sure what I think, even now," she admits.
"Even in the piece I'm don't say 'I can't believe Fearne did this' or whoever. A lot of them are my mates.
"I've just never come near this world before, never even thought about doing a shoot before. I've always taken my role at CBBC so seriously at all times, I'm very much a goody two shoes in the class, and I knew about my responsibilities.
"Basically, it comes down to choice and whether it works for you, for all the reasons I explore in the documentary."
Kirsten's exploration of the lads mag world starts with researching the likes of FHM, Loaded, Nuts, Zoo and Front and attending a topless photoshoot where cover girl Amii Grove gives her some tips.
Kirsten's sense of humour shines through - she has performed as a stand-up comedian for a number of years - and while it's an attractive characteristic, she can't rely on it to help make her look sexy.
"I don't take myself very seriously," she says.
"That's part of the problem here!"
As Peter Stringfellow tells Kirsten when she goes to see him and a couple of the dancers at his London club, it's impossible to be sexy and funny at the same time.
She dances for the nightclub owner in an attempt to prove she can stop laughing long enough to look good on the podium.
Unsurprisingly, it doesn't go well.
"That was quite interesting! I embraced the challenge of it, there's no point forming an opinion on something unless you've explored it a little bit," she explains.
"The girls I met were lovely too, really friendly and helpful. That's not to say I could do anything by the end of it!
"What's not explained in the documentary is when you see me run upstairs to do my dance for Peter Stringfellow, I've got the most ridiculous tutu on. I was trying to figure out what to wear, and someone said 'Peter's here and he can't wait' so I had to run upstairs, wearing the tutu, but still with with my jogging bottoms on underneath.
"I did want to try properly, I didn't want to mess about, so when Peter started laughing at me I was upset," she continues.
"There was one point when I shouted at him, 'Peter, man, you're not taking this seriously' but he carried on laughing. So much so that I decided to stop.
"I did genuinely try, although it might not look like I did!"
Kirsten was born in Middlesbrough, but her family moved around the world when she was growing up due to her dad's work as a civil engineer. At various times, they lived in Algeria, Kuwait, Singapore and Nigeria.
Despite that, she's managed to hold on to her north eastern twang, which gets stronger the more animated she gets.
It's clear Kirsten's family are very important to her, and during one of the documentary's uncomfortable moments, she's filmed asking her dad what he thinks about her doing a magazine shoot.
"I had eczema all over my neck before that chat," she says.
"What my family thinks is a massive influence, always has been. My dad's phoned me in the past and said 'I didn't know you were in the Daily Express' or whatever, and it'll be because I didn't know I was going to be."
Kirsten's slight suspicion of the media began when she was starting out in TV. While she was auditioning for SMart, the CBBC art show she has presented since 1999, her mum died.
She subsequently appeared on the cover of a newspaper, which was published at the same time as a family wedding, shortly afterwards.
"That's why I've never done much press over the years," she says.
"I feel a responsibility within my family not to disgrace us O'Briens!"
As Kirsten discovers, thanks a series of video diaries within the programme, her career crossroads has come about due to the death of former colleague and close friend Mark Speight, who died just over a year ago.
"If you'd have told me before I did the documentary that I'd end up talking about my mum and Mark, I'd have said 'I won't. What's it got to do with that?' but it's amazing what things come up when you're in a strange situation.
"I've ended up feeling very proud of the film because it's so honest, but I never would have anticipated it ending like it does."
Kirsten still admits to being at a turning point with her career - you'll have to watch the documentary to see if she goes through with the shoot - but plans to increase the amount of stand-up she does.
She's also started doing bits of presenting work for BBC's The One Show alongside her good friend Angellica Bell.
Angellica was also a CBBC presenter, but made the move to mainstream TV after her lingerie-clad shoot for FHM in 2007.
"I still don't know what to do next," says Kirsten, finally.
"But at least I've crossed something off the list now."
Kirsten O'Brien - Extra Time
Kirsten first started broadcasting when she was a student at Birmingham Polytechnic (now University Of Central England). This led to a job at Tyne Tees television in 1995.
She began presenting on CBBC in 1996 and became known for her on-screen partnership with Otis The Aardvark.
Kirsten played Peter Pan in pantomime in 2004.
She performed her own stand-up show at the Edinburgh Festival in 2006 called Lesley's Lunch Hour - Not During Lunch, And Not Quite An Hour.
She holds the world record for wearing 42 socks on one foot.