Can I take action to make my ex-wife assume the mortgage on the home she lives in but I legally own?

Is there a time limit set out in the divorce order for her to complete the refinance? Hopefully there is. A complete review of your order will be required to give you a complete opinion on what can be done. It is likely a matter of contempt. You should do something before the home slips into foreclosure, because the bank doesn't care about your divorce order and will not necessarily wait on you to work it out in court with your ex.

Why would there NOT be a provision that she re-finance the home if she was the one keeping it? Was this some sort of Do-It-Yourself divorce?

It seems as though you represented yourself in this case and that is now causing you a problem. If an attorney was representing you, it is likely that they would have asked the judge to place in the final order that she was to refinance, do a loan assumption or obtain a new home loan to buy the property so that the property could be in her name and ownership only. The attorney would probably have also asked that it be placed in the order that you not sign a quit claim deed giving away your interest in the home until such time as she had placed the mortgage in your name and you are no longer legally liable for the home loan. Since none of this appears to have been placed in the order, no, you cannot now force her to refinance the home. She is free to let it be foreclosed on if she likes. It wasn't even placed in the order that you all will agree to sell it within a certain period of time. Therefore, it seems like you can't make her do anything because it was not placed in the final judgment and decree of divorce. That's why we urge people to hire an attorney, not because we want to take your money, but because anything not in the final divorce paperwork you are unable to change at a later date. You are stuck with it.