Praise be to Allaah.
There is nothing wrong with paying the zakaah on jewellery on
the basis of estimation, if the person thinks it most likely that he has
paid the amount required. For more information please see the answer to
question no. 145091.
You mentioned in your question that she used to pay zakaah,
but you are not sure about the manner in which it was paid. If that is the
case, then the basic principle is that she was paying zakaah in the manner
which would discharge her obligations, and your uncertainty does not affect
The basic principle is that if the Muslim has performed an
act of worship, then it is valid and acceptable unless there is any proof to
Based on that, the heirs do not have to pay zakaah on the
jewellery for the past years. But if you want to do an act of kindness
towards her and give some money in charity on her behalf, then the reward of
that will reach her, in sha Allah.
And Allah knows best.