Here is all the info, straight from the manufacturer:
Hepatitis C Treatment-PEGASYSŪ (Peginterferon alfa-2a)
Yes, the side effects look horrible. No treatment at all appears to be even worse.
"PEGASYS is a medicine used to treat some adults who have viral hepatitis C or hepatitis B who show signs of liver damage with no prior treatment with interferon. PEGASYS is also used in patients coinfected with hepatitis C and HIV. PEGASYS works to reduce the amount of virus in your blood, helping your body fight the virus.
Most Serious Side Effects for PEGASYS
PEGASYS (Peginterferon alfa-2a), like other alpha interferons, can cause fatal or make life-threatening problems worse (like mental, immune system, heart, liver, lung, intestinal and infections). Your doctor should monitor you during regular visits. If you show signs or symptoms of these conditions, your doctor may stop your medication. In most patients, these conditions get better after you stop taking PEGASYS (see medication guide for more information and warnings)."
There are also several discussion sites on the subject.
Have you talked to your Pharmacist about this medication - or your mother's Physician, at length?