What Causes Numbness Around The Lips Of A Child Post Oral Chemo Treatment?

My 7 year old daughter says her lips are numb. She has no muscle spasms or any other symptoms apart from a cough, sore throat and the corners of her mouth being split. Yesterday it hurt her to open her mouth, naturally, due to the sores, but today she opened her mouth and said she can t even feel the pain from them. Her medical history is Nephrosis, diagnosed as minimal change disease after a biopsy, and Interstitial fibrosis of the kidneys. She had an 8 week course of oral chemo last year, predated by 2 years on prednisolone, which she stopped responding to.