Thanks for providing more information.
Firstly cyst in shoulder can result in pain in shoulder blade.
However as she has positive RA factor so this itself alone doesn't indicate Rheumatoid arthritis.
Positive RF test results may also be seen in healthy people and also in people with kidney disorders.
Further blood work like Quantitative RA factor, HLA-B27 test, ANA, CRP, Anti-CCP, ESR should be done to rule out Autoimmune disorder.
As she has family history of SLE so risk of getting auto immune disease are high as it can be hereditary/genetic.
Rheumatoid factor may also be elevated in chronic hepatitis, any chronic viral infection, dermatomyositis, infectious mononucleosis, systemic sclerosis apart from systemic lupus erythematosus (SLE).
So further a referral to Rheumatologist should be considered.
And if it is initial stage then it can be treated well rather than considering wait & watch approach.
I hope this helps.
If you have any further query then feel free to ask.
Positive feedback and bonus are highly appreciated.