A 65-year-old female presents to her general practitioner's office complaining of sudden-onset right arm pain. She recounts a recent incident while performing light gardening tasks, where she felt a distinct "snap" in her right upper arm, immediately followed by discomfort and a visible change in her arm's contour. Since then, she has noted difficulty with everyday activities requiring elbow flexion and shoulder abduction, such as lifting groceries or reaching overhead. Her past medical history includes type 2 diabetes mellitus, controlled hypertension, and hyperlipidemia. Medications include metformin, lisinopril, and atorvastatin. On physical examination, there is noticeable bruising around the deltoid insertion, and palpation reveals a distinct, globular swelling approximately 5 cm superior to the antecubital fossa, consistent with a "Popeye" deformity. Active elbow flexion against resistance is graded 3/5, and active shoulder abduction is 4/5, both eliciting pain. Based on this clinical presentation and physical findings, what is the most likely diagnosis and the appropriate initial management strategy?