You can find her correspondence at Project Gutenberg. And you can find some of her theological treatises at Intratext. From her treatise on prayer:
Then that soul obeyed and rose out of herself, in order to learn the true solution of her difficulty. And the Eternal God said to her, "In order that you may the better understand what I shall say to you, I shall revert to the beginning of your request concerning the three lights which issue from Me, the True Light. The first is a general light dwelling in those who live in ordinary charity. (I shall repeat to you here many things concerning these lights, which I have already told you, in spite of My having done so, in order that your creeping intelligence may better understand that which you wish to know.) The other two lights dwell in those who, having abandoned the world, desire perfection. Besides this I will explain to you your request, telling you in great detail that which I have already pointed out to you in general. You know, as I have told you, that, without the light, no one can walk in the truth, that is, without the light of reason, which light of reason you draw from Me the True Light, by means of the eye of your intellect and the light of faith which I have given you in holy baptism, though you may have lost it by your own defects. For, in baptism, and through the mediation of the Blood of My only-begotten Son, you have received the form of faith; which faith you exercise in virtue by the light of reason, which gives you life and causes you to walk in the path of truth, and, by its means, to arrive at Me, the True Light, for, without it, you would plunge into darkness.
