Answer: The prayers must be performed in their proper order. First, she makes up the missed prayer, then she performs the one whose time is presently in.

Prayer of a Woman Who Is Unveiled
Question: Is the prayer of a woman who is unveiled—i.e., not wearing the ḥijāb—in the presence of unrelated men valid?
Answer: If what is meant by “unveiled” is that her face is uncovered, then her prayer, in and of itself, is valid. However, she incurs sin for exposing her face, because a woman is obliged to cover her face from unrelated men, as established by numerous evidences from the Quran and the Sunnah.

Covering a Woman’s Head for the Prostration of Recitation
Question: At times I recite the Quran with my head uncovered. If I come across a verse of prostration, should I prostrate without a head covering, or should I cover my head first and then prostrate?
Answer: You should cover your head before performing the prostration of recitation (sajdat al-tilāwah), since some scholars regard it as a form of prayer that inherits the rulings of prayer. Covering the head is therefore the more cautious and preferable course. Allah knows best.