Sizing - it is best measure her feet in cm and add 1 cm bigger. If it is 11 cm, then go with 12 cm
For soft sole measurement:
Size 2 - 0-6 mos 11 cm
Size 3 - 6-12 mos 11.8 cm
Size 4 - 12-18 mos 12.6 cm
Size 5 - 18-24 mos 13.4 cm