Hi, I'd like to help you with your question.
It sounds like your friend is depressed and has PTSD, as you said. The trauma she suffered is not yet resolved and can take a number of years to work through. Abuse goes to the very core of a person, making them believe they are worthless among other things. Crying is your friend's way of expressing the emotions that are still there.
Crying can be good. It is a way of letting out those feelings that otherwise sit inside and hurt us further. If your friend did not cry, she would either express her feelings in other ways such as anger or she would withdrawal.
Your concern for your friend is valid. She should address her feelings and come to terms with what happened to her. But everyone works through things at their own pace. And PTSD recovery is slow because the trauma is so deep and hurtful.
Consider that her current therapist may not have been a good match for her. Searching for a good therapist is much like looking for a doctor you can work with. Sometimes you need to see a few before you find one you can work with. Before she gives up on therapy, your friend should attempt to see another therapist.
While you cannot convince someone to seek therapy who does not want to, you can encourage your friend by being open and honest about the behaviors you see her exhibit that concern you. Telling her that crying all of the time is not typical behavior. And encourage her by telling her another therapist may be more helpful to her than her previous one.
Also, offer to go with her to see her new therapist. Even if it is just one time, you can have the opportunity to express your concerns. If that is something she rejects, you can always contact the therapist before her appointment and tell them your concerns. They cannot respond back (confidentiality), but at least they will be aware of your perspective.
The best way to find a new therapist is to ask for referrals. Have her talk to her doctor about who he/she recommends. Also, she can ask friends or family. She can also search on line and get a better idea of what the therapist is like before she makes an appointment. Here is a link: http://therapists.psychologytoday.com/rms/.
Offer to help your friend through self help. There are numerous resources she can use to help herself work towards recovery. Here are a few to get her started:
The Post-Traumatic Stress Disorder Sourcebook: A Guide to Healing, Recovery, and Growth by Glenn R. Schiraldi
The PTSD Workbook: Simple, Effective Techniques for Overcoming Traumatic Stress Symptoms by Mary Beth Williams and Soili Poijula
She can find these books on Amazon.com or her local library may have them for her.
I hope this has helped you,