It could also mean that she spent a significant part of her life with him, and she cherishes her time with him, even if it is over. I find that when I mention my exes to a current or potential partner, it is in terms of a particular memory that has meaning to the conversation, or to explain something about myself that may be a result of an event with him. If the relationship ended on good terms, I'd say there is a chance that she is looking back fondly, but it doesn't necessarily mean she isn't open to moving forward with someone new.
Maybe ask her? If she is defensive, she may have left-over feelings that she doesn't want to admit to...if she is embarrassed. She probably didn't even realize she was doing it. I'd give her the benefit of the doubt, but, either way, you need to know for your own sake.