Pretty sure Optoms have to Bulk Bill, they sign an undertaking when they get their first provider numbers they will as they get a pretty big Medicare fee back from the government. If not, they are not supposed to charge you higher than the rebate you will get I think?
If she has a lazy eye, I would ask the optom to write you a referral as well. Kids frames are fantastic these days!!
You can get a second opinion, it is helpful to the Optom to know that you have been somewhere else and seeing them for a second opinion so they bulk bill you the right item number, as alot of the Optom Item numbers can only be used once every two years.