The St. John's Wort may not be sufficient in cases of severe depressive disorder. It is mostly used for mild depression.
The antianxiety medication would only target the anxiety not the mood. It may be helpful to have her see a psychiatrist to assess for antidepressant medication.
Other things that can be looked into would be whether or not her depression worsens around her cycle as this could be PMDD. If she had not had her thyroid checked or had a full blood panel test, it would be a good idea to have these done.
Not sure which therapist determined that her depression is not severe enough. If she does not have a regular counselor, connecting with someone is going to be beneficial besides medication management. Depression can be caused by different factors and determining the correct ones can lead to proper treatment. You're not doing anything wrong as you're searching for options to help her.
Try to encourage her to go out and engage in certain activities. Even if it is going w/ you to the store or for a brisk walk.