Hi,
I have mid level Hospital cover with Medibank and there were some out of pocket expenses for my mastectomy in 2012, however as your mum has top level cover she may have less to pay, or receive a higher benefit.
My expenses were: 1) Hospital Excess: $500 (this is paid once per calendar year, so any subsequent hospital admissions do not attract an excess charge, so the admissions for chemo, done privately also, were all at no charge), 2) Surgeon's fee: I chose to go with a particular surgeon and he provided a quote prior to the surgery of $2,090, but after Medicare and Medibank refunds was out of pocket by $708. 3) Anaethetist's fee: Out of pocket: $272.
As Robyn suggested, chat with the surgeon and ask for a quote upfront. The surgeon's office can confirm if they can "no gap" the surgery, or provide a quote, and usually have an idea of what Medicare / Medibank rebates are available. Hope this helps. Wishing your mum all the best.
Jane