When imaging (ultrasound and/or CT and/or MRI) shows a solid mass in some specific areas of the body, the chances that it is cancerous are very high. Only a pathologist's examination of the tumor or a small piece of it (biopsy) can tell for sure if something is cancerous. However, when imaging shows that the chances are very high that a mass is cancerous, it is not unusual for a gyn oncologist to proceed without a biopsy. If the tumor is deep in her pelvis, it can be difficult to do a biopsy, and there are some very serious reasons not to attempt biopsy. During surgery, the doctor can see the tumor, and a bit of it is sent to the pathologist for an immediate examination. The doctor will know before he proceeds with removing the tumor whether it is cancerous or not, and if it is not cancerous, the doc will most likely remove the mass and as little normal tissue as possible; if it is cancerous, surrounding tissue must be removed, too.
I understand her concern about fertility; I myself had my only child at age 40, and endometrial cancer at age 50. Has she discussed her concerns about fertility with her gyn oncologist? See http://www.cancer.org/docroot/MBC/MBC_2x_Fertility_and_Cance , http://www.asrm.org/Media/Ethics/FertilityPreservation.pdf&n http://www2.mdanderson.org/depts/oncolog/articles/06/1-jan/1 or some infomation about cancer and fertility. I know that there are some research institutions that are beginning to preserve fertility in new ways; perhaps her gyn oncologist can put her in touch with these researchers.
It is more important to do surgery correctly (for her) than quickly, but of course, you don't want to wait too long. One of the articles linked to above points out that some gyn oncologists are not good about telling patients their options for preserving fertility. I, myself, got a second opinion before my surgery (I lived in a small city where there were no gyn oncs); I had to wait three weeks to get an appointment but it was worth it for the information I received. She may well need to go outside the Kaiser network to get the information or or treatment that will preserve her fertility. At 37, her fertility is naturally in a steep decline, which is does not bode well for the success of fertility preserving options, but so many great things are being done now that someone may have some hope for her.