All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
It is lawful for you to marry this girl as she is not one of your Mahaarim (i.e. plural of Mahram, who is a person whom one is permanently prohibited from marrying due to suckling, marital, or blood relations) from family lineage, unless both of you suckled from the same breastfeeding mother, in which case, it becomes forbidden for you to marry her.
Allah knows best.