Hi hydrocarbion,
your priority should be about getting some quality instruction and worry about equipment later.
You should know that not all kites develop the same power for the same size between various models and brands. Ultimately choosing a small kite size or a small board will make more sense in stronger winds and a slightly larger kite size and board will make more sense in lighter winds. The difference between 18 and 25 knots is pretty big especially for a light weight rider.
For a 62 KG beginner in Perth, you should consider a 7M or 8M kite and approximately a 135cm board. Below is the kite size/board size chart we display on our website as a guide for our customers. At the very early stages of the her progression, a larger board (140-145cm) might help especially in lighter winds (18-22 knots). In our school we always give students larger boards to help them progress much faster. Once the technique and stance is good, larger boards are no longer necessary. Also, as a beginner, having a bit more power is always helpful so getting a 8m kite now make sense, and maybe 1-2 years down the road a 7m kite is she gets enough experience and skill. Better technique means more efficiency which translates in using smaller size kites and smaller size boards.
Hope this helps
Christian - KiteBud