Is she physically and mentally able to play with 18 year olds? A lot more goes on both on and off the field at the varsity level that your child and the parents have to handle. Is the team tight knit and the coaches good? Ask yourself these questions before deciding some parents do not want their 14 year olds doing 18 year old things. Will it make her a better player I think it depends on the coaches and how are the JV coaches? If the JV coaches are weak then the move to varsity is warranted cause when she does get playing time she will know what the varsity coaches expect. Give it a lot of thought though.