Answered by Sayyidi Habib Umar bin Hafiz (may Allah protect him and benefit us by him)
What can we do to discourage convert sisters from wearing makeup?
First of all, we should strive to make faith firm in their hearts so that they taste the sweetness of faith. We should let them mix with other sisters who have left things like makeup. We should teach them about the lives of the Mothers of the Believers and the daughters of the Prophet ﷺ so that they then come to venerate these great women. We should convey to them the true meaning of honour and nobility that Allah has accorded believers both male and female in what He has legislated for them. We should convey to them also that the hijab and modesty are a means of honouring and protecting a woman.
We should not talk about the issue directly in the first instance but rather we work on establishing the foundations of their faith. Each individual is different so we must take this into account. Some will take longer than others to leave these things. The Prophet ﷺ taught Mu`adh to call people in stages: first to call them to faith, then to prayer and then to zakat.