I get my husband to talk for me sometimes- not all the time as I am a true extrovert- but sometimes on bad days and drive throughs! He doesn't mind at all. But if she is using you as a crutch that can become old rather quickly. I don't have the answer to your problem but I think that this may be something to explore with a trained professional. Someone who can get down to the bottom of her insecurities in a safe and productive way. You love her obv and the best way to love someone is to empower them to love themselves. I also think that you are absolutely right in not wanting to talk for another person, it severely impedes their growth and experiential learning, and consequently your growth and experiential learning. I hope that you can both find someone to truly help you. Good luck.