Overall I'd say that there isn't enough strong female characters in Berserk, and tbh I never saw Caska as one(well except for the first half of the eclipse). Caska is mostly used as a device to makes Guts' quest move forward. First he abandonned his revenge to take care of her, then this whole quest to Elfhelm is motivated by his wish to find a safe place for her, but mostly because he wants to cure her. Caska is also one of the reasons Guts won't forgive Griffith for what he did, she was also the tool Femto used to hurt Guts. She's pretty much a tool at this point.
Only a few females like Luca strike me as strong, her interaction with Nina and her attitude back at Albion makes me think that. Flora is certainly wiser but overall she didn't get enough screetime. And Schierke while being a "strong" witch, she's still a kid. Before she met Guts she knew nothing of the world, the human world. Basic things eluded her,like that time at Vritannis(the scene with the Kushan that were executed). I guess it's the result of living a secluded life with Flora, she never really interacted with people let alone kids of her own age. And the trio with her, Isidro and Isma now is kinda annoying.And I don't like the fact that Schierke is becoming so important to the story, and to Guts in general.
Farnese is the only female character who started very weak, but slowly became strong. She's willing to follow her own beliefs, now that she isn't a zealot anymore. She still has her insecurities but overall she's the female character who had the most character development imo.