Hi @Alyssa Hall. Yes. If you have the user's email address, you can sign her up by creating an account for her using her email address, then share the password with her. She can log in using her email and the password you have picked, then she can change her password by clicking on her avatar> Account Settings> Reset Email> Save.
In order to be able to sign her up manually, you need to make sure that the registration settings of not "invite-only". Change it "public", create the account for her, and then if you want you can make it "invite-only" again.