Hi Kathleen, it is absolutely normal for your mum to feel depressed after surgery. I was in a severe depression episode four months after completing radiation and chemo. I had to seek help from psychiatrist and anti-depressants. Support from family is very very important during depression. Make sure you give your mum the right support and if you cannot handle your mum's depression,please do get help from medical professional before it gets worse. Take care.
Karen.