Explanation

Sumayyah binti Khayyat (R.A) is historically recognized as the first martyr in Islam after Hazrat Khadija (RA). Lubaba bint Haris (R.A) is not widely cited as the next woman to embrace Islam after Khadija (RA). Ummay Aimen (R.A) embraced Islam, but Sumayyah's status makes her a more likely answer for this specific question context. None of these is incorrect because Sumayyah was indeed an early convert and martyr.