The character of Ro Laren is a peculiar one. Originally she was set to join up with then-Commander Benjamin Sisko on Star Trek: Deep Space Nine but the actress playing the Bajoran, Michelle Forbes, didn’t want to go from a recurring character to a series regular due to the amount of time needed to film.
That’s when the change was made to have her go from joining DS9 as Sisko’s number one to joining the Maquis with the idea of her joining Voyager. While we can’t find any other source at the moment to back this up, Trek Culture did in fact claim that one pre-production plan was to have the now-Maquis defector join up with Chakotay, B’Elanna Torres, and Tuvok on the same ship that was featured at the start of Voyager.
The change however would keep it as a recurring character rather than a series regular. Ideas were tossed around of her either dying in the opening episode or two, or write in a subplot that has the Federation turncoat transported away so that she could come back every so often.
This would be the same idea they’d ended up using for a Maquis-turned Cardassian spy in Seska. Seska was original with the Voyager crew but she would end up falling in with the Kazon.