Hello, my name isXXXXX and I have over 20 years of experience as a veterinarian.
I am sorry to hear that poor Trixie is having symptoms of disc disease.
Unfortunately dachshunds do have a predisposition to back problems.
Ideally she should be on a non-steroid anti-inflammatory, and a muscle relaxant if needed, but I highly recommend something for pain too, such as Tramadol, which you are already using. In some mild cases rest alone and pain medication may be enough. Since I haven't physically examined her I cannot tell you what medication or dose to give her, especially as she hasn't been prescribed anything by a veterinarian, but I can direct you to an accurate webpage that will give you dosing information and side effects for Tramadol. http://www.petplace.com/drug-library/tramadol-hydrochloride-ultram/page1.aspx
Please read this closely before giving her any more Tramadol.
She should be closely confined. No stairs, running or jumping. If you have a crate for her I highly recommend using it. The less she moves around the more comfortable she will be and the faster she will heal. She should go out on a leash to relieve herself. You will need to confine her for several weeks, even as she starts to feel better or she may reinjure himself. I think the reason that she isn't getting better is because as she starts to heal she overdoes and reinjures herself. Keeping her on the thin side is recommended to decrease stress on her neck and back.
You can also apply a heating pad set on low/medium to her back several times a day to relieve painful muscle spasms.
If you are interested in reading more here is a link to an excellent article about intervertebral disc disease, its causes and therapy: http://www.petwave.com/Dogs/Dog-Health-Center/Bone-Joint-Muscle-Disorders/Intervertebral-Disk-Disease/Symptoms.aspx
Long term for joint pain I do recommend using a combination of a
glucosamine/chondroitin product (examples are Dasuquin or Cosequin) and an
omega 3 fatty acid (like 3V Caps or Derm Caps). These work synergistically and
improve cartilage health and joint fluid quality and quantity as well as reducing inflammation. They can take several weeks to see full improvement but some dogs do very well with them alone. They are available over the counter.
Another option is a product called Duralactin. This is an anti-inflammatory product derived from milk proteins and it also has omega 3 fatty acids incorporated into it which can be very helpful. See this link for further information: http://www.duralactin.com/products_canine.htm
There are other less common causes of back pain such as infections, tumors of the vertebrae or the spinal cord itself or fibrocartilagenous emboli but far and away disc disease if the most common cause of back pain in dogs.
Please let me know if you have any further questions.