Is it considered a sin for a fasting woman to inform her non-Muslim colleagues at work about the arrival of the iftar meal?

It is not permissible for a Muslim to help someone who is breaking their fast during the day in Ramadan—whether Muslim or non-Muslim—with food and drink if their breaking of the fast is without a valid excuse. This is because it constitutes cooperation in sin and transgression. Scholars have explicitly stated the prohibition of providing drink to a Dhimmī during the day in Ramadan.