Does not the wording in Surat Ahzaab verse 59 suggest that the Prophet Muhammad (s) had multiple daughters rather than just one?
"O Prophet! say to your wives and your daughters and the women of the believers that they let down upon them their over-garments; this will be more proper, that they may be known, and thus they will not be given trouble; and Allah is Forgiving, Merciful." - Qur'an 33:59
In Quranic verses, plural was sometimes used for one person like in the Verse of Mobahala ( Sura Aal Imran; verse 61) ( Let us call our sons and your sons, our women and your women, and ourselves and yourselves) The Prophet (SAWA) called Fatima only for his women and called Ali only for ourselves.
Authentic evidence supports that Fatima was the only real daughter of the Prophet Muhammad (SAWA) while had three fostered daughters who were orphaned daughters of Hala Bint Khowailid sister of Lady Khadija (AS).
Justice of the Prophet (SAWA) will never allow discrimination in dealing with the three fostered daughters wihle all the focus of the Prophet was on Fatima.
Wassalam.