There is no way out under your circumstances. The best way is that you get divorced from your ex, get married to your girlfriend and she applies for spouse visa from within country. All this must take place before her current visa runs out.
Other way could be, that she goes back to her home country before her visa expires. When you get divorced from your ex, she either arrives in UK on fiance visa, marries you here and then gets a full spouse visa. After your divorce, your can visit chile, get married to her there and then she applies for spouse visa from chile.
In any of the above situations, you need to be earning a minimum of £18600 per year gross.