I've been trying every combination I can think of on Google - pink diary ... pink princess diary...
I think if it's a cheapo game like they sell at the dollar store - or Family Dollar it would be close to impossible to find. :(
I DO think that it probably is early - mid 90s though... and who knows if the little girl got it new?
I know on a Disny Board I frequent someone posted the picture yesterday... so it IS getting out there..
I have exhausted all my options on google/ebay/etc. I am sure you are right about the knockoff idea and the fact that that toy is circa 1990's. I just hope someone will recognize it and it helps.