Shoe challenge: most versatile ballet flat for tweens (formal)

[twowhat?]

DDs wanted to do Cotillion next year. It starts in January. DD2 has special needs for her shoes - one of them has to be lifted because her right leg is nearly 2 inches shorter than her left. There are 6 nights of Cotillion and she will need 6 different outfits (formal dresses, basically). Because it's expensive to add in these lifts, I want to get her a SINGLE pair of flats that will work for all of the nights. They need to be comfortable but also versatile and work with a variety of formal dresses/colors. I am thinking either a nude flat or a nude-ish metallic (like a beige-y gold-ish) so that she can wear with both dark colors and light colors (haven't bought the dresses yet but that's easier). The sole MUST be split-able (the cobbler will split the sole in order to add in the lift in the center - "sandwiched" by the original sole - and allow her to maintain the same tread on both shoes) so rubber is easiest but this cobbler can do almost anything. Since her lift is so high, a wider, flatter sole is better for stability - no wedges or she will totally twist an ankle. I'm looking everywhere and am willing to purchase multiple pairs online from FS/FR stores or stores easy to return in person to. A sole that is the same/similar color to the shoe is less conspicuous and would be preferred...DD2 is already fretting about how "stupid" she'll look.

Something with straps would be extra nice because the lifts do add some weight and straps would help keep the heel from slipping off, especially if she wears hose. Something like these from Amazon maybe? Is this cute for tweens and not silly?

Any recommendations to help my search would be awesome!! She wears a women's 6.5-7. It takes about 2 weeks to do the custom lift and Cotillion starts mid-Jan so I'm starting to sort of panic!