One of the reasons that the Romans were so successful at enlarging their Empire is that they knew when to leave well enough alone. After the dust settled they generally left the newly conquered locals pretty much alone. A new governor, maybe some other officials. New taxes. But they left local government on its own, offered military careers to the men and mostly importantly, left the local Gods and Goddesses alone.
The Romans were pretty much happy with their own Gods and did not care about converting anybody else. By leaving the local gods, priests and rituals in place they sidestepped a lot of problems. They also showed little to no interest in those local gods.
But Epona was a different story. Goddess of the horse, a Celtic warrior in her own right and a fertility Goddess, the Romans were quite taken with her. So much so that they took her back to Rome and set her up on the altars of their own Gods. She didn't seem to mind and became part of everyday life in Rome.
The Celts honored several warrior goddesses, Epona, Rhiannon and Brigid are some of the better known.