Casio watches for a small wrist
Quick note on measurements
All measurements will be shown in millimeters. The first number will be lug-to-lug width, the second number is case diameter, and the third number is watch thickness.
G-SHOCK models that fit the small wrist
There are unfortunately not too many G-SHOCK models that will properly fit smaller wrists. There are some who say "just get a Baby-G model", but I can assure you that is not a good solution, because many women's models are too big for the small-wristed just like the men's models are.
Measurements: 48.5 x 43.0 x 14.77 mm
This is still available for under 50 dollars and is the standard G-SHOCK "square". In photos this looks small but it's not. Bear in mind it's almost 15mm thick.
The DW5600E fits small wrists easily, but the only problem you may encounter is "strap gap" if your wrist is thin and flat. Strap gap is when the watch sits on your wrist, but the strap leaves spaces on either side that may cause some discomfort.
Measurements: 46.7 x 43.2 x 12.77 mm
This looks almost identical to the DW5600E, but that's in appearance only. This model has many more features (solar power, atomic timekeeping and so on,) and is in fact notably smaller than the 5600. Lug-to-lug is shorter and it's a full 2mm slimmer.
This model is considered by many small-wristed fans of G-SHOCK to be the perfect size.
Measurements: 48.5 x 43.0 x 14.70 mm
What makes this particular model excellent for smaller wrists is the fact it has a factory nylon strap, which completely eliminates the strap gap problem for those with flat wrists.
If the only thing keeping you from getting a G-SHOCK is the resin strap, then you want the DW9052V. It appears to be larger than the 5600 square but in fact is almost identical in size.