Unfortunately, The Walking Dead since season 4; she's played a central role in several storylines but hasn't been put to good use in the war with the Whisperers.
The Walking Dead began a new story for Rosita after the time skip in season 9 by revealing that Rosita - who has continued to spurn the affections of Eugene (Josh McDermott) - had a brief relationship with Siddiq (Avi Nash) and is now romantically involved with Gabriel (Seth Gilliam). In season 9, Rosita and Eugene became the first characters to discover the Whisperers, and this was the moment that set the stage for the storyline that's about to finally be concluded on The Walking Dead. Later, Rosita had a child and began raising her with help from Siddiq (the child's father), Eugene, and Gabriel.
Not much has happened with Rosita since then. The Walking Dead hasn't really done much for Rosita in season 10, though to be fair, it did give her a few stand-out moments, such as her heated Dante (Juan Javier Cardenas) infiltrating Alexandria and killing Siddiq.
Eugene, who appears to be a crucial piece of the story that will introduce the Commonwealth, has also had Rosita and help move him in the direction he needs to go. Having Rosita reject him is what sent him to Hilltop, where he eventually made with Stephanie. Later, it was Rosita who encouraged him to meet Stephanie and get help for their people.
So why did The Walking Dead season 10 only use Rosita to advance the stories of Eugene, Siddiq, and Gabriel, when she's easily important enough to the show to have her own arc? The Walking Dead could have made her much a bigger part of the Whisperer War by having her directly involved in their efforts to defeat them. It's too late for that problem to be adequately fixed, but hopefully the series will provide Rosita with something meaningful to do in season 11.
With Michonne (Danai Gurira) gone, Alexandria could use someone like her to help fill the gap and assist Gabriel in leading the community. What The Walking Dead will do with Rosita will be interesting, considering that the comic book version of the character never made it this far. For the Commonwealth arc, The Walking Dead will need to create a brand new story for Rosita, one that will, hopefully, use her properly.