Stratification:

Based on IOTA simple rules, there is one "M" feature - irregular solid tumor and no "B" features.

ADNEX model: 74% benign.

O-RADS Category 5: high risk (>50%) - "Solid lesion with irregular outer contour, any size, any color score".

Histology:
Adult granulosa cell tumor. 
Ovarian capsule intact, no lymphovascular invasion.
FIGO stage I
TNM pT1NxMx
Fallopian tube normal.

Discussion:
This is an irregular, large solid mass which clearly requires excision.  The patient's young age and normal CA 125 provide some reassurance

Granulosa cell tumors are generally solid tumors with variable appearance. The typical feature of multiple small cystic locules - "Swiss cheese appearance" - is perhaps present here, but not pronounced enough to suggest the diagnosis. The endometrium was not well assessed in this case, but can be thickened in association with granulosa cell tumors, which are often estrogen producing.