Simple past "she found her keys" relates an event in the past. Present perfect "she has found her keys" describes an event in the past with an impact on the present (now she can drive...). Past perfect "she had found her keys" an event in the past that impacted on a later event in the past (then she could drive...). This may be more suited to ELL. – Jon Hanna Feb 12 '13 at 16:46