Hello,
What your sister is having is cheek wrinkle or a lower cheek wrinkle more precisely. Your sister can consult a cosmetologist and discuss the option of dermafillers. Other treatment methods include prescription acid creams or peels, stronger retinoids such as Retin A, Botox( botulinum toxin) ,non invasive or carbon dioxide laser and a surgical facelift.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.