The Prophet had four daughters.
Why did Holy Prophet PBUH took only one daughter in Mubahila event
against christians while Allah ask in a plural way. Come lets bring your
sons and our sons, your females and our females.
The verse of Mubahalah was revealed when a delegation from Najran met the Prophet and disputed with him about Isa عليه السلام.
قال ابن عباس : هم أهل نجران : السيد والعاقب وابن الحارث رؤساؤهم
Ibn Abbas said: They are the people of Najran : Saeed, Aqib and Ibn Harith were their leaders
— Tafsir al-Qurtuby
قال: نـزلت في العاقب والسيد من أهل نجران، وهما نصرانيان
He said: This was revealed regarding Aqib and Saeed who were from the people of Najran, and they were Christians
— Tafsir al-Tabary
The delegation came in 10 AH:
وفيها قدم وفد العاقب والسيد من نجران
This year came the delegation of Aqib and Saeed from Najran
— Tarikh Tabari ; سنه عشر (Tenth Year of Hijrah)
None of the other daughters of the Prophet, other than Fatimah, were alive at this time.
Why only one daughter is the leader of all females in heaven? Isn't it
injustice with other daughters and Prophet can never do injustice.
I don't understand your logic here. Why do all the daughters need to be equal in their excellence and virtue? Is not Yusuf عليه السلام of a higher rank to his brothers, despite them all being the sons of Yaqub عليه السلام?