Severe grades of acne (nodulocystic type + scarring) will not respond to oral antibiotics - Accutane is considered the only "cure". Depending on the severity of your daughter's acne, it's very important to seriously consider taking it since it can minimize further scarring and disfiguration (will not treat any scarring that's already present).
It sounds like your dermatologist has given you a good review of the potential side effects: must NOT get pregnant, theoretical risk of moodiness, increase in triglycerides etc. The most commonly experienced side effect is systemic dryness (dry skin/lips/eyes) - but this usually only last for about max 1 year after stopping the drug. There isn't really a toxic effect on the liver (unless there is heavy alcohol intake at the same time).
Bottom line, if acne has affected your daughter's self-image and the acne is severe, Accutane is a good choice.