Is 53 kg according to an 18 year old girl too much?

A colleague of mine had not checked her weight for couple of months but knew that she was getting fat..her previous weight was around 48 kg around 6 months back,and now its 53 kgs..is that considered to be bad according to her age,as people tell her that it is just part of growing up..and what should she do to reduce her weight..?