My dog has swelling to her right rear ankle,...

Hello, I am sorry to hear that Beauty has swelling to her right ankle.
Did this seem to come up quickly?
Is she running a fever or has she even run a fever when her ankle was swollen (rectal temperature more than 103.5F)? If so have antibiotics been tried?
Is the change in the radiograph to the bones or the joint space itself? Does it seem to affect more than one bone? Does she or has she ever had more than one joint swollen?
If there is any increase in joint fluid or joint "space" an aspirate and cytology and culture of the joint fluid may be very helpful and is less invasive then a bone biopsy.
Are ticks a problem where you live? If so a tick panel may be helpful as tick borne diseases, like Lyme disease, can cause joint swelling and inflammation.
While bone cancer typically occurs in older dogs it is a cancer that can be seen at any age.
If she has never had a fever, ticks are not a problem where you live and the joint fluid aspirate and cultures (for both bacteria and fungi) come back negative a biopsy is the best way to diagnose her condition. Identifying the particular type of tumor she has, if that's what she has, is very important in prognosis and directing therapy. It is not something we do lightly but sometimes it is the only way to get a diagnosis.
Let me know if you have any further questions.

Thanks for the further information.
I am very glad she is felling well and heartworm and gastrointestinal parasite negative.
Slight anemia and slightly low thyroid levels can simply point to stress of dealing with another health problem. It is very likely that if her joint problem is diagnosed and treated those values will return to normal.
With most malignant bone tumors (like osteosarcoma), as well as invasive infections, the blood levels of calcium rise so a slightly low calcium is actually a good sign. Without knowing how low her calcium is it may be a normal level for her as we are all individuals and slightly low may be perfectly normal in some individuals.
I highly suggest at least an aspirate, cytology and culture of her joint fluid as well as a tick panel if ticks are a problem around you if possible before a biopsy. These tests are much less invasive and may give your veterinarian some answers.
If her joint space isn't enlarged and it is impossible to collect joint fluid and tick borne diseases simply aren't a problem around you then logiaclly the next step is a biopsy. It will be the only way to get a diagnosis and thus a treatment plan.