You only have to sell or liquidate the house if the court that issued the divorce decree says that you do. Based on what you have shared with me, it sounds like you have a very solid equitable argument that the house should not be liquidated. If the court orders the house to be liquidated, based on your payment for the house alone, you have a very strong argument that you should not have to give up 70% of the value of the home.
Of course, what is relative to the house and division also has relevance in view of the rest of your property and monetary division of marital assets. If you had any distinct advantage relative to division of other marital property, then she could leverage you on the house before the court and get the desired 70%. Moreover, if she worked to put you through school prior to purchase of the house, then she may be able to leverage this amount.
In short, there are many factors in play here, including the temperament and preconceptions of the judge. However, based on what you have told me alone, it does not appear that she would be in a favorable position to leverage liquidation of the house and receive 70% of the proceeds of the house.
Please rate my answer positively and let me know if you have any other questions or comments.
Best wishes going forward!