Thanks for the query. Dont be panic. Most probably it seems to be muscle sprain
. Was there any injury
to shoulder? Need to ask her? tumour or infection is relatively rare conditions to happen. I would suggest to get her examined by an orthopaedic doctor and he may suggest Xrays and if needed MRI
of the region. Also blood counts and ESR
gives fair information if any thing wrong going on in the body. Thanks.