The problem that I see with pretty much all the suggestions made so far is that the figures that we paint are not really intended for kids.
I don't just mean in the sense of them having a lot of bare flesh showing. These are - for want of a better description - "adult toys", and to be honest I can't see delicate resin and white metal accessory parts lasting 2 minutes without breaking off in the not-so-delicate hands of your average 5 year-old. Quite aside from the fact that some of them are quite challenging to assemble (never mind paint) even in skilled adult hands. Then there's all the nasty toxic tools of the trade like superglue, primer spray cans, thinners etc. That's on top of the filling, sanding and other prep work often involved.
There is a reason why manufacturers put labels on their boxes like "Not recommended for children under the age of 12" (Alpine) or "This is not a toy. Not for sale to minors under 14 years of age" (Scale 75) or "High-quality kits for collectors" (Pegaso).
I have to agree with Patrick (maya8) above. Disney princesses, poster paints and such like are the best way to go for now. Forget about buying her the kind of figures that we paint. Otherwise be prepared for frustration, disappointment, tears and putting her off figure painting before she's even got started.
In the end it's your call of course. But the way I see it is that there's plenty of time for her to graduate to this kind of stuff when she's older - assuming she's still interested and this isn't just the fleeting fancy of a young child.
- Steve