How can I help my girlfriend who may have ptsd? She has to overcome her demons?

Be with her. While you can't cure her, you can be a source of care and comfort for her. You can also encourage her to seek counseling for what she's experiencing. In psychotherapy, there are very helpful treatments such as emdr and others. Sometimes medications can also help with symptoms like anxiety & depression that can come with ptsd. A psychiatrist can help with that part & collaborate with therapist.
Plant a seed. You have received excellent input from quite a few panelists. Your girlfriend may or may not elect to overcome her demons. Fear of tackling the demons can become somewhat paralyzing. Avoidance is part of the disease. The most you can do is love her, support her & encourage her to accept help. You may plant a seed but she will determine if it will grow.
PTSD. You can encourage her to see a psychologist. Ptsd, if left untreated, only gets worse.
Help her get help . Help her get psychological help to evaluate, verify the diagnosis & formulate a treatment plan. Psychotherapy can be very helpful in resolving the aftereffects of a traumatic experience. Medication may also be included for part of the process. Ur very important role is to be the most supportive, loving & encouraging boyfriend that u can be... Wishing you both well!
See a therapist. The cause of the ptsd is important to find out and then tailor the treatment according to ti.