A covenant is a legal issue, similar to an oath. In the context of the quote, the covenant refers to God's covenant to his people through the blood of Christ. Meaning the spiritual family you have in God, the people who have made the same commitment and sacrifice, is stronger than the tie with your biological family. This is especially true for people on countries where Christians are shunned by their families and killed for belief. Many people end up having to leave their families, not because the church forced them, but their families forced them. Friends will come and go with time, family will turn on you for ideas, but people who sacrifice everything for what they believe will always have a bond.
I hate her family using the “blood is thicker then water” quote, especially when it’s used out of context.
The full quote is actually, “the blood of the covenant is thicker then the water of the womb”
meaning the friends you make along the way are deeper bonds then the family you happen to be born with