Praise be to Allah.
It is permissible for the daughter to give her zakaah to her father if she is not able to spend on him, in the sense that the wealth that she has is little and barely covers her needs and those of her children, and is not sufficient to spend on him too.
In this case, it is permissible for her to give zakaah to her father; in fact giving zakaah to him is better than giving it to someone who is not a relative, because the Prophet (blessings and peace of Allah be upon him) said: “Charity given to the poor is charity, and that given to a relative is two things: charity and upholding the ties of kinship.” Narrated by at-Tirmidhi (658) and Ibn Maajah (1844); classed as saheeh by al-Albaani in Saheeh Ibn Maajah.
But if she can afford to spend on him, then it is not permissible for her to give zakaah to him; in this case, she must work out how much she gave of her zakaah and give it again, to the poor.
Ibn Qudaamah said:
Zakaah should not be given to parents and grandparents, no matter how far the line of ascent reaches, or to children and grandchildren, no matter how far the line of descent reaches.
Ibn al-Mundhir said: The scholars are unanimously agreed that it is not permissible to give zakaah to one’s parents when the giver is obliged to spend on them, because giving zakaah to them would mean that they no longer need him to spend on them, and spending on them would be waived, so the benefit of that would come back to him, and it would be as if he had given it to himself, so it is not permissible. This is like paying off his debts with it.
End quote from al-Mughni (2/482).
Al-Bahooti (may Allah have mercy on him) said in Kashshaaf al-Qinaa‘ (2/294):
If he gives zakaah to someone who is not entitled to it… because he is a relative, in the line of ascent and descent of the giver, or one on whom he is obliged to spend because he will inherit either an allocated share or as a residuary heir, and he is unaware that this recipient is not entitled to it, then he finds out about that, he has not discharged his duty (of paying zakaah). End quote.
See also the answer to question no. 105789.
But if what was given to him was zakaah on the husband’s wealth, then it was given appropriately, because the husband is not obliged to spend on his wife’s father.
See the answer to question no. 170811.
And Allah knows best.