Should my mom take us-guided fine needle biopsy for detection of a possible suspected gallbladder cancer?

YES: No meat no treat. If there is no tissue biopsy done to establish/confirm the diagnosis, it will difficult to start anybody of treatment like chemotherapy. Other option if possible is to remove the gallbladder. Discuss with your surgical oncologist /oncologist the best way to do.

Depends: If it is a needle biopsy of the gall bladder itself than most providers just take out the gall bladder vice just a needle biopsy of course every person has individual issues that complicate a blanket statement. If the biopsy is an area outside the gall bladder like a lymph node of liver then it is a good idea.

Follow MD's advice: There in insufficient information to provide an informed opinion. Please follow the advice of your doctor who knows your mom better.

Ask ?: I would always follow the advice of your doctors. But you may want to ask if their suspicion is high enough to just warrant a cholecystectomy.