I can appreciate your difficulties and fully empathise with you and your niece.
I hope you understand that an advanced melanoma
means the cancer has spread from where it started to another part of the body.
The treatment of her condition is highly specialised & is going to be by a team called a Specialist Skin Cancer
Multidisciplinary team that includes specialist surgeons and cancer doctors, a specialist nurse, an occupational therapist, camouflage make up specialist, and a counsellor or psychologist
The actual treatment might be in form of injections, surgery or by radiation
that will be best planned by the team in consultation with you.
Please try not to panic , accumulate courage & prepare yourself and your niece for upcoming days. Try to improve her general health by giving good nutritious food till you see the doctor and keep her morale up.
Hope you find the information useful.