I agree with the above poster.
Your girlfriend may also want to talk to her Dr about hormone therapy if that's possible. You did'nt say why your girlfriend had the surgery. If it was for cancer then hormones are most likely not an option.Taking replacement hormones may really increase your girlfriends libido.
Losing libido after hysterectomy is something common for women. I would suggest you to start talking about this with your girlfriend, try to be supportive and to comprehend with her emotions. If you both feel that you need more help I would suggest a vista to someone specialized , maybe a sexologist. Wish everything will be ok soon