The divorce charges depends on case by case and regarding the time needed to finalize a divorce also varies, is it contested or uncontested divorce and etc?
Why dont't you call a few lawyers to clear your doubts and know what are your mummy's rights?
This law office offers free phone consultation. Take advantage of it to understand how to help your mummy.
Their legal executive, Elin is very patient and understanding.
Their website is at http://sgdivorcelawyer.com/ and their phone number is 6850 5411.