She said: "Verily, I seek refuge with the Most Gracious from you, if you do fear Allah."
This means that when the angel (Jibril) appeared to her in the form of a man, while she was in a place secluded by herself with a partition between her and her people, she was afraid of him and thought that he wanted to rape her. Therefore, she said,
إِنِّي أَعُوذُ بِالرَّحْمَن مِنكَ إِن كُنتَ تَقِيًّا
(Verily, I seek refuge with the Most Gracious from you, if you do fear Allah).
She meant, "If you fear Allah," as a means of reminding him of Allah.
This is what is legislated in defense against (evil), so that it may be repulsed with ease.
Therefore, the first thing she did was try to make him fear Allah, the Mighty and Sublime.
Ibn Jarir reported from Asim that Abu Wa'il said when mentioning the story of Maryam,
"She knew that the pious person would refrain (from committing evil) when she said,
إِنِّي أَعُوذُ بِالرَّحْمَن مِنكَ إِن كُنتَ تَقِيًّا
("Verily, I seek refuge with the Most Gracious from you, if you do fear Allah."