Any mass of unknown origin that is growing warrants a clinical examination. Common things being common, the mass could possibly be a lipoma, leiomyoma, fibroid tissue growth, or a cyst. While all the above listed conditions are benign, the possibility of the mass being a malignancy cannot be ruled out. Therefore, a careful clinical exam by a physician is warranted to rule out the possibility of a life threatening condition and, if clinically indicated, additional studies such as imaging or biopsy might be necessary.
On the topic of insurance, most public hospitals have clinics set up for patients without insurance. If your sister in law doesn’t have insurance and is a candidate, then the option of those clinics should be explored.