My servant is Christian and I want to help her to enter Islam? When I talk with her about Islam, she asks me give her something to make her trust me.
Praise be to Allah, the Lord of the World; and blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
Your offering some money or other valuable things to this Christian servant in order to attract her to Islam and eventually convince her to become Muslim is a good act that is rewarded, if Allah wills.
It is reported in the sound Hadith that any person who attracts someone to Islam and they become Muslim by their hands, such a person gets a great reward for that act.
The Prophet said to Ali: "By Allah, if one man is guided on the right path (i.e., converted to Islam) through you, it would be better for you than (a great number of) red camels" [Reported by Imam Muslim].
Red camels are among the best things Arabs like to possess.
Allah knows best.
You can search for fatwa through many choices