I don't see a point in a Caldina unless you need the extra space it provides. An Altezza is a comfortable car, and the advantage is that it has probably more space interior space than an RX-8 with conventional 4 doors as well.
The RX-8 would be my pick amongst the 3 though, as its a relatively new car with nice leather interior and sporty looks, a perfect chicks car. It isnt too fast in a straight line, but it handles pretty well and is overall very good bang for buck imo.
The downside to a DC5R is that being a type-r, it is probably subject to higher theft rates as compared to an RX-8. The recaro's, gearknob, badges and whatnot are all in high demand in the 2nd hand market. Although it is definitely a better driver's car as it is faster in every way, comfort is slightly sacrificed.
I guess what im trying to say is that if your sister is just looking for a reliable semi-sporty car to use daily, RX-8 is the pick. But if she values performance above all else, then go for the DC5R.
In the end, just get her to drive em before she makes her final decision :D