What do I need to file now that the defendant has filed her own motion for custody with points and authorities?

If you filed an action for sole custody, but no motion, and your ex filed a motion for custody in your action, you file an opposition, with or without a countermotion, to which your ex can file a reply.  Some forms are on the self-help center website, but if you do not know what to do or how, your best bet may be to hire a family law specialist to assist you.