Property in Spain

My ex-partner and I jointly own a large property in Spain. We split up 3.5 years ago, she returned to UK and I’ve been living in the house, running it and keeping it maintained alone since then. We have been trying to sell the property since the split, constantly reducing the price with no sale.

After purchase of the property we both invested in having a pool built and reform of a joined rental accommodation ammounting to around 50,000 euros. In the latter stages of the building work my partner put in a further 17000 euros, to complete the work. She is now demanding this exact amount back from the proceeds of a sale, in addition to the normal 50/50 split on completion and in fact threatening to not sign any contract of sale if I don’t agree.
In the current market we both stand to lose a considerable sum on our investment, we jointly paid 150000 with a current outstanding 57000 euro mortgage and invested a further 50000 on improvements. We’ve just had an offer of 125000, first in 4 years. We both need to sell and accept the losses.

Regarding the 17000 extra she put in, surely there should be a degree of proportionality here mainly with respect to the dramatic fall in property prices during the last 8 years, also she wasn’t forced to leave but she couldn’t have stayed here anyway due to health problems and non – adjustment to Spanish way of life etc. I’ve been here keeping things afloat, for the benefit of both of us maintaining the property, running a holiday rental for which she has gained 50% of the income with little or no input whatsoever on her part. I’ve been living on a small company pension and and half the income from the rental and paying all the bills, including those from the rental. I could go on but just wanted to substantiate my claim that she is being ”unreasonable” in her demands.

I don’t know what she has in terms of evidence or proof of her 17k investment, is that really relevant but in order to show goodwill I would be prepared to negotiate a compromise on that figure because the last thing I want is for this to get out of hand and drag on, involving solictors which takes time and money we can ill afford to pay.

As I think my ex partner is being unreasonable in her demands. What is my legal position on this? Initially, how much would it cost to send her a letter stating my willingness to come to a compomise and afford an amicable agreement as any form of communication between us is now extremely difficult?