It may just be me but you said in your first post what i try to get across to people all the time!
I can understand RTR's but do i like them is another thing! I find spending more will save less... And buying new i also find abit hard to understand for example buying a new chassis every year when the previous car chassis only came out 11 months before... Anyway i would suggest telling her about 2nd hand. I priced up a Cougar SV pro + electrics on here for just over £200 , now seeing as thats a competive start he can only get better..
If it was me at the age 8 and i had a new car (RTR) and boom somone hits me , and my turn buckle has gone to shot, it would put me off... Might just be me in my competitive nature.. not to sure