A learner calls حَمْرَاءُ alif maqsurah merely because it is feminine. Which correction is accurate?

Alif al-Ta'nith: Maqsurah and Mamdudah

• It is maqsurah because every feminine word ends in ى.
• It is mamdudah because its written ending is اء.
• It has no feminine marker because hamzah cannot mark feminine.
• It uses ta marbutah because it is an adjective.