Is expiation (kaffarah) obligatory for the days the questioner did not fast when she was young, especially since she is a university student and does not possess any money?

If a girl reaches the age of nine and experiences one of the signs of puberty, she is considered an adult (baligha) and is bound by Islamic rulings such as prayer and fasting. Missed Ramadan fasts after puberty must be made up (qada'). Expiation (kaffarah) for delaying the make-up fasts becomes obligatory if the delay was without a valid excuse and she was aware of the ruling, and it remains a liability until it is paid. However, if she was unaware of the obligation to make up the fasts, no expiation is due from her. The missed days must be made up before the next Ramadan. If Ramadan arrives and there are still unmade-up days without a valid excuse, then expiation for delaying is due for each day.