I suspect i have spyware on my pc?

my daughter was recently a victim of identity theft, she very rarely shops on line,does not recieve statements only uses cash points from inside banks etc. she recently brought gig tickets using my pc 2 weeks later someone made 2 small transactions then a big one for £600 but they was able to give her name address,account number including the 3 digits on the back of her debit card this was spotted and her account was quickly cancelled.for her to be a victim of ID theft the only way i see it possible of this happening is that i have spyware on my pc.
i dont know much about computers i run AVG anti virus but from what i understand this will not pick up spyware, so what do i do to get rid of it.