Sit down and have a heart to heart with her. I’d suggest for you both to come up with a list of strengths (what you like about each other) and opportunities for improvement for each person. This will help open up your lines of communication more and cause self-reflection. Also, this gives her an opportunity to speak too so you can maybe gain a better understanding of her side / struggles (if any). If she does bring up confidence as an issue, then respond by asking her how you can help and maybe you two can brainstorm ideas on how to address it. Be a good listener.