Will need more information.
How are you administering the Tylan? Injecting into breast or are you dosing her down the throat?
Also need to know how much you are giving her at a time.
Seems like I have the best luck using Tylan-200 and doing 1/4cc into the breast muscle. I had a really sick silkie that I was doing this treatment twice a day though only once is recommended I think. Seeing you are using Tylan-50, I would maybe figure at least a 1/2cc into the breast muscle, alternating sides each day.
Of course, if whatever she has is not treatable with antibiotics, its either Viral or Bacterial that is not cured with antibiotics, I do not recall which, it might just have to run its course.