Islabikes do pink now, and it is quite a nice colour too.
They have a size chart so you can check size, but if she’s growing out of a 12″, surely she’d fit on a 16″?
People seem to go 14″ to 20″ and skip 16, so it doesn’t necessarily mean an extra bike.
Could you take the pedals and stabilisers off the 12″ bike and make it into a balance bike when you get the new bike and then not bother with stabilisers, know a few kids, mine included who went straight from balance bike to pedal bike and skipped the stabilisers, I wasn’t sure I believed the whole balance bike to pedal bike thing would work before I saw it happen, but it was <30 minutes from getting the pedal bike to going 100m without being held.