I don't know the context of her initially opening up to you (both of you having serious conversation, her having a few drinks and feeling loose, her being upset at you, or her just randomly started talking, etc.) but the main thing is to continue to communication.
Tell her that you are not upset at her for what she said about you, and that you are actually glad that she was being frank with you. The main thing is to make her feel comfortable and let her know that her feedback (even constructive criticism) is welcome and lets you know areas that you or the both of you need to work on. No matter what she says (even if it does upset you), do not react right away in a manner that will cause her to resent her having spoken her true mind. Just make her as comfortable as possible.