Are the daughter's savings with her father (which may not be returned) counted with the father's money when calculating Zakat, or are they considered independent, knowing that their total reaches the Nisab, while her money alone does not reach the Nisab?

It is not permissible to revoke a gift, unless the giver is a parent and the recipient is their child, based on the Prophet, peace and blessings be upon him, who said: "The one who revokes his gift is like the one who vomits and then returns to his vomit," and his saying: "Except for a parent regarding what he gives to his child." If you genuinely gift money to your daughter, such that she can dispose of it freely, then it does not fall under your zakatable assets, and your taking from it when needed does not harm. If the daughter's wealth reaches the threshold for zakat (nisab), she is obliged to pay it. If she is an adult and mature, she pays zakat herself. If she is not an adult or not mature, then the parent must pay zakat from her wealth.