Are you looking for a Road Bike? Hybrid? MTB? City Bike?
For a road bike, you could either go with 24" (520) wheels or 650c wheels.
Fuji Ace 650 would be a possibility. Somewhat cheaply made, but you could upgrade it as needed.
Trek used to make some nice WSD 650c bikes, but I think they've dropped the products. Used ones might show up if you're hunting.
This Diamondback Podium 650 looks like a little nicer than the Fuji Ace.
Diamondback Podium 650 Youth Junior Women's Road Bike Ultegra Velocity 49cm TT | eBay
Oh, it looks like Giant has a little mini-Cyclocross bike.
Giant TCX 26 CX junior youth kids cyclocross gravel road bicycle bike | eBay
NOTE:
It looks like the little Giant is $710 new, so I'd offer quite a bit less for the abused one. Giant may also sell those direct to international customers which might help.
https://www.giant-bicycles.com/us/tcx-espoir-26
For a "city bike", the Soma Buena Vista Mixte comes in a 26"/650 size. Although it appears to have a fairly long effective top tube length.
Buena Vista Frame Set | SOMA Fabrications
If you wish to go with a cheap MTB, there should be a pretty good selection of kid's 24" MTBs.