What would you say if she wanted to spend $850 on some cute Jimmy Choo shoes?
http://www.bergdorfgoodman.com/store...Id=prod6140036
$300 on a phone is not so bad I think, it's not "spoiled" if she payed for it myself.
Personally I think $ 850 for shoes is too much, but I think under $500 is ok

if it's for something classic you can wear over and over again.