One way to tell if you have a successful character arc

There is a very good way to tell if you have a successful character arc for your main character.
Look at the first scene, look at the climatic scene. Did your character possess all the skills to be able to successfully complete the climatic scene in the first scene?  Or would she have failed spectacularly? How did she have to change/transform ? What was it necessary for her to learn? If she doesn't have to transform or change, you don't have a character arc.
In a romance, particularly a series romance that transformation must be directly influenced by the hero. In other words, the main agent for change for the heroine will have been her growing relationship with the hero. If she changes for some other reason, it is probably a story with romantic elements, rather than a romance.