Is it permissible to say "Amen" after Christians pray for me for blessings, enlightenment, or similar things?

"Ameen" means "O Allah, respond [to our prayers]." It is permissible for a Muslim to say "Ameen" to a disbeliever's supplication for good, just as the Prophet, peace be upon him, was responded to when he replied to the Jews with "wa alaykum" (and upon you). Inviting non-Muslims to Islam requires knowledge and insight. The caller to Islam must first solidify their knowledge and creed before engaging in argumentation with them, especially a young woman in the prime of her life, who should focus on building her religious and academic foundation first.