A 14-year-old nulligravid female is brought to the ER by her parents with a 12-hour history of severe, intermittent left lower quadrant pain. She has had nausea and vomiting for the past 2 hours. On history, the patient experienced menarche at age 12 and denies past or current contact with a sexual partner. Her last normal menstrual period was 3 weeks ago. On examination, she is afebrile, pulse 100, BP 110/70, respiratory rate (RR) 20. She is visibly uncomfortable. She has no costovertebral tenderness, has diminished bowel sounds, her abdomen is nondistended, and exhibits rebound and guarding in both lower quadrants. She is unable to tolerate a pelvic examination due to pain. Laboratory values are as follows: WBC 13, HCT 39, -hCG (-), UA (-). Apelvic ultrasound shows a normal nonpregnant uterus, normal right adnexa, and an 8-cm left adnexal mass with a 3-cm solid component.
Which of the following would be the next appropriate step in managing this patient?