Your partner paid taxes on 50% of the profit and absorbed (on a tax basis) 50% of the losses. Those Schedule K1s are evidence of a 50/50 ownership of the property.
I do not have any idea how much equity you have in the property, but you only paid 38750.00 for it so it cannot be a huge amount. Let's use 38750.00 as your equity amount, just for an example. 50% of that would be 19375.00. 31.43% would be 12179.00. The difference between the two is 7196.00. Its quite possible that you would spend more on legal fees than 7196.00 and quite possible that you would lose, therefore wasting that money, because she has the Schedule K1s that show that she has been treated as a 50% owner.
If your equity is less than 38750.00 it makes it even more likely that it would be a waste of money to litigate it. I agree with the others that negotiation is your best option, but if I am right that the equity is 38750.00 or less, there isn't much point in fighting it if she insists on 50%

