All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
If the questioner had no valid excuse to delay the fasting of the days that she missed in Ramadan until the following Ramadan came, then she has to repent to Allah for that. She also has to make up for all the days of fasting that she missed in Ramadan, in addition to the observance of the expiation prescribed for such delay. The expiation is to feed a poor person for each fast that she delayed after its due time.
It should be noted that the expiation is not repeated by the repetition of delays over years. The expiation is observed only one time for each day of fasting that she delayed. As long as the questioner is able to fast, then she is not exempted from fasting, even if she is sick. This is because the sickness for which fasting is replaced with the feeding of the poor must be chronically incurable.
The fast of the missed days is not required to be immediately done all at once, according to the predominant view. Nor has the fasting of the missed days to take place consecutively. The questioner can fast as is possible. She could fast one, two, or three days every once in a while and according to her ability until she finishes all the days that she missed. If she had a valid excuse to delay the fasting of the days that she missed in one Ramadan until the following Ramadan came, then she is not required to observe the respective expiation. She is only required to make up the days that she missed in such case.
It is worth noting that fasting the days that one misses in Ramadan takes precedence over voluntary fasting such as the fasting of the six days of Shawwal.
Allah knows best.