My wife is an impulsive buyer and spends a lot of money without thinking twice. Am afraid we are not saving enough. How do I explain her?

Maybe both of you can sit and and list out all the expenses that needed to pay. And from there let her know nicely that perhaps she need to try to save a little to ensure that you all have enough to spend without getting into debts. Bring her for a counselling if she need professional help. Anyway just sit down and talk nicely I'm sure you guys would find a good way to settle the issue.