IMDB says much the same thing: "After appearing in
"Star Trek: The Next Generation" (1987) as Ro Laren, she was approached to play the same character in a starring role on
"Star Trek: Deep Space Nine" (1993). When she turned down the part, because she didn't want to commit to a regular TV role at that point in her career, a new Bajoran character, Kira Nerys, was created and
Nana Visitor was cast in that part."
Doing a series is a major chunk of your time: each episode represents about a week of filming, so for roughly 26 weeks a year you are completely unavailable for other projects, and those 26 weeks happen to be in the time when everyone making movies most wants to be filming, too. Peirce Brosnan lost the gig as James Bond the first time because Remington Steele got renewed, and filming for the show and the movie overlapped.
DS9 came out in January 1993, which means they were filming in 1992, which is the same year she was appearing on TNG as Ro.
And in 1993 she was in at least 2 movies, one of which had her starring opposite David Duchovny, so you can see why she thought her career was headed in that direction. She had done two years on a series, a few single episodes, a handful of episodes in one season of TNG, and now she was being offered movies, and she thought that was where the future lay.
Who can really blame her: medium-big name stars get millions of dollars for 6 weeks of filming on a movie, where most TV stars make a tiny fraction of that. And it isn't like those 2 movies in 1993 were a flash in the pan: 2 more in 1994, 3 in 1995. It wasn't until 1996 that things started to cool down (one feature film, one TV movie, and one episode of The Outer Limits, which is still pretty good).
Update: IMDB also has this quote from her:
On turning down
"Star Trek: Deep Space Nine" (1993): There were all sorts of rumors about why I didn't take [the DS9 role] and that I was quite arrogant about the whole thing. It wasn't that at all. It was, again, about wanting variety in my career. If I'd gone on to do DS9, I might not have had the variety I've been lucky to have in my career. That's not to say I wasn't grateful for the opportunity; I genuinely was. However, I had to make a choice that felt right for me, which was a difficult one, especially as a young actor being offered a steady job. (TV Zone Magazine, January 2005)