Is it permissible to pay monetary compensation for breaking the fast on behalf of my fiancée who has diabetes, and what is its value in Egypt, and is it permissible for me to pay it on her behalf before the official engagement?

Insulin injections do not break the fast. The fidyah (expiatory feeding) is obligatory for those who are permanently unable to fast. According to the majority of scholars, it is not permissible to give the fidyah as a monetary value, based on the verse: {And upon those who are able [to fast, but with hardship] - a ransom [as substitute] is feeding a poor person} (Quran 2:184). It is not valid to give it except after its obligation becomes due with the dawn of the day. It can be given daily or for several days combined after they have passed. It is permissible to appoint an agent to give it, and it is not a condition that it be from the patient's own money.