We could call Him the Creator, the Almighty, or even Number One. In Arabic the name used is Allah. Obviously the name varies in every language.
The rest of the Bible deals with what God is like, and dozens of references to the love of God in the Psalms (Psalm 136 for example has God's steadfast love in every verse) prepare us for the NT statement that God is love. The content of what God's kind of love is like is brought to us from heaven by the Son of God who explained it and lived it for all to see in the Gospels.
The difference between Christian faith and Islam is not a different name.
The question is whether God is like the God of the Gospels, or like the God of the Qur'an. In one picture God is a loving oneness of three Persons held together by love, in the other God is a solitary unitarian entity. In one God loves us and welcomes us to His family just as we are. In the other only those who meet the requirements set out in the Qur'an make it to the rewards of heaven, and all others burn in hell for ever.
Having said that, it seems that many who call themselves Christians
really picture God in the same way as God (Allah) is pictured
in the Qur'an. That means it is not the name but what God is like that
is at issue. If your friend began talking to God as a loving parent, a
friend who knows the worst about her and loves her just the same, or the
Holy Spirit who is willing to give all the wisdom and love that she needs,
then her prayers would be addressed to the same kind of loving God as yours.