I listened to Terry Farrell’s Delta Quadrant podcast interview, and I sympathize with her. I think Jadzia Dax is a very difficult role to play even for a veteran actor, because this character has memories and experiences spanning multiple lives. Yet Farrell found herself in a situation where she had to play one of the most difficult roles in the show even though she was one of the youngest and thus least experienced actors in the cast.
In terms of a base performance, tuning in on the age of the character may have been difficult. However, I find that some of Farrell's main failures as an actress came under circumstances that were more or less humanly relatable. In Dax, she feels guilty about a transgression and wants to preserve the honor of a former love. In Invasive Procedures, she is facing death. In Equillibrium, she is dealing with memory recovery. These were all standard tropes in television at the time DS9 aired.
I also think that much of what she says in the podcast is inconsistent. You can read this whole thread where I point out to instances in which Farrell's own words seem to contradict what she says about the difficulties of the character. That said, context matters, and she is trying to make her way into the convention circuit, often sitting next to people who felt she had been very unprofessional. Farrell wants to portray herself in a postive light, encourage the adulation that many fans have for Dax, but also have cordial relationships with her former costars. If I may say, she was the "odd old man out" among people with extensive stage experience. Avery Brooks set a serious, professional tone for the set, which worked well for Auberjonois, Shimerman, Visitor, and Meaney, but which was alien to Farrell, a model with acting talent (and I think it is fair to say she had some talent). She may well have been used to work environments that were more accommodating. Now, there is some speculation in what I have written. Nonetheless, putting herself out in public might present its own challenges, making it more difficulty to speak her mind.