I don’t know if you are aware of the story of Zaid (ra), the adopted son of the prophet. Ibn Umar (RA) reported that after the Prophet (saw) freed Zayd ibn Harithah and adopted him, people used to refer to him as Zayd ibn Muhammed until the verse the following verse was revealed,
“Call them by (the names of) their father’s, that is more just in the sight of Allah…” (Al-Ahzab 33:5)
Once this principle became part of the divine law, the Prophet was instructed to further emphasize it by a series of warnings. For example, on one occasion he said,
“He who knowingly attributed his fatherhood to someone other than his real father will be excluded from paradise.” (Bukhari, Muslim, Abu Dawood)
Leave her name as it is , sister. It’s only a surname. It has nothing to do with who he is financially providing for her.