You want to know how to do this right....
Do you have a Payless Shoe store in your area? They run BOGO (buy one get one free) specials all the time. Offer to buy them some new summer shoes while you go buy yourself a pair.
I wouldn't turn down a shoe shopping offer- and be even happier if the guy purchased my shoes!!!!
This would be my reaction........

And you would get what you wanted too....her shoe size.