Rights of a landowner in case of encroachment

Dear PAO,

My friend and I purchased a 300-square-meter (sqm) lot. Based on our agreement, we will divide the property equally; she will be entitled to 150 sqm, and I will be entitled to the other 150 sqm. Before the partition, she asked for permission to begin the construction of her house on our co-owned lot, which I granted. When we finally decided to partition the lot, we discovered that her house encroached on my part of the lot. My friend strongly insisted that she should only pay me the value of the specific portion of the lot because she did not know of the encroachment. What are the options or remedies available to me as co-owner of the lot? Can my friend insist on purchasing the encroached portion of my land?