What is incumbent upon my mother who has not paid Zakat on her money for more than 15 years, knowing that the Nisab for silver is 595, and she currently owns 47,0 Riyals? And is Zakat obligatory on worn gold that reaches the Nisab?

The question is vague, but it is understood that the questioner's mother was unaware of the obligation of zakat on money, believing it was exclusively for gold and silver.

If her ignorance was due to negligence, then the zakat for past years does not fall away from her, as ignorance is not an excuse in all cases, and zakat does not expire with time.

So, she should pay the zakat on her money starting from the first lunar year in which she owned the nisab. The nisab is estimated by the value of the lesser of the two currencies (gold or silver), which is more beneficial for the poor. Thus, the nisab for money is what equals 595 grams of pure silver.

If she knew the Sunnah and the amount, she should act accordingly; otherwise, she should act with caution. If all her money is in the bank, she can request an account statement to know the balance each year.

As for jewelry intended for permissible use, there is no zakat on it according to the majority of scholars.