DO you still like her? If so, then why not just tell her that you still like her, and that the argument was no big deal?
Or don’t even mention the argument (since it was no big deal), just call her and say something like, “Hey, I was just thinking about you and wanted to call and say hi,” and just put the whole argument behind you, and move on to other (happier) topics of discussion. She’ll figure out soon enough that still like her if you’re willingly calling her and cheerfully having a conversation with her. But if you start talking to her less (as you say you’re doing), then naturally she’ll think you don’t like her as much anymore.