Jazmine,
Thanks for the questions. Sorry to read of your mother's ordeal.
I would summarize your mother's case by presuming that she developed a staphylococcus aureus bloodstream infection. This type of infection would explain the fever, flu-like symptoms, weakness, and the swollen knee. The timing of the infection is most consistent with the cath procedure being the portal of entry for the infection; this type of infection is a known, but uncommon, risk of the procedure. The elderly are particularly susceptible to this infection.
The hands numbness is more confusing, and I can't comment further without examining your mother. Bilateral hand paralysis would be a rare complication of either staph infection or a cath procedure. The doctors probably thought, as would have I, that the numbness was from the prolonged placement on the table -- especially given your mother's history of neck disease. Steroids would be a potential treatment for this type of numbness, but I am not a neurologist so my comments must be taken with a grain of salt. Certainly, no physician wants to treat a patient with steroids in the midst of infection, but sometimes it must be done.
Hope that helps. Good luck.