All perfect praise be to Allah, The Lord of the Worlds. I testify that none is worthy of worship except Allah and that Muhammad is His slave and messenger.
Your friendship with this girl does not take you out of the fold of Islam. The prohibited Walaa’ (taking disbelievers as allies) that drives a Muslim out of the fold of Islam is when he likes and befriends a disbeliever for the sake of his disbelief. However, befriending a disbeliever for the sake of obtaining a worldly benefit does not fall into the category of the prohibited Walaa’. Nonetheless, taking Muslim friends is better and yields better outcomes.
Allah Knows best.