The Prophet, sallallaahu ‘alayhi wa sallam, said, “Whoever fasts a day for the sake of Allaah, Allaah will keep him a 100 year distance away from the Hellfire.” Can the fasting of the days that a woman missed in Ramadan be considered as fasting for the sake of Allaah?

All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.

The wording of the Hadeeth that you mentioned in your question is different from the one cited in the Hadeeth collections. The authentically used wording as narrated by Abu Sa‘eed Al-Khudri reads, “I heard the Prophet, sallallaahu ‘alayhi wa sallam, say: ‘Whoever fasts a day for the sake of Allaah, Allaah will keep his face seventy years away from Hellfire.’” [Al-Bukhari, Muslim, At-Tirmithi, Ibn Maajah, and An-Nasaa’i; this is the wording of Al-Bukhari]

There are different views concerning what is meant by the Prophet’s statement, 'for the sake of Allaah'—whether he meant the fasting observed while performing jihad in the cause of Allaah or that he meant fasting that is sincerely observed for the sake of Allaah.

In his commentary on Sunan Ibn Maajah, As-Sindi stated:

When the Prophet, sallallaahu ‘alayhi wa sallam, said in the Hadeeth, “…for the sake of Allaah…” he referred to sincerity and dedicating the fast to Allaah alone. It is also possible that he referred to whoever fasts while fighting in the cause of Allaah, which is more likely to be meant here.

In Faydh Al-Qadeer, Al-Munaawi said, "His statement, ‘whoever fasts a day for the sake of Allaah,’ either means that one seeks the pleasure of Allaah alone by such fasting or that one fasts while he is performing jihad or Hajj.”

That being said, the implications of the Hadeeth can be extended to fasting the days that one misses in Ramadan, if such fasting is observed with the sincere intention of seeking the pleasure of Allaah alone. This is based on the explanation that suggests that fasting for the sake of Allaah, as mentioned in the Hadeeth, means to sincerely dedicate the fast to Allaah alone. 

Allaah Knows best.