Kindly educate me on what should be done by a woman owing previous ramadan, now its another ramadan, what can she do to repay or she just forget about it.

Someone asked me today is feeding a poor person obligatory on those that can't afford it? Should they only fast?

And, what if the person is old and poor but sick due to chronic illness or age and can't fast any longer. What is the ruling?

She should make up for the missed days later as well as feed a poor person for each day with a quantity of one sa' approximately three kilograms of the staple food of her particular area. This could be three kgs of rice, dates, etc according to the food of that land.

As for those who cannot feed a poor person then the rule would fall away Inshaa’ Allah because Allah said,

"Allah burdens not a person beyond his scope." [1]  

An old person who can no longer fast or a chronically ill person has to give food to a poor person for each day.

Reference:

[1] [Qur’an 2:286]