It would surprise me if the frustration was not just as intense for her as well as for you. I have yet to see a child this age who did not want to learn and be successful--she sounds like she's really having a tough time. If her skills are truly on level of a child in pre-K, then this sounds like more than just a memory problem. Discrete memory problems are fairly rare unless there is a neurological issue. Most times what looks like memory problems are actually problems with encoding new information (paying attention to it, storing it in working memory) or retrieval problems (the information is stored but the person has trouble accessing it--you have experienced this when you try to think of the word you want to say but cannot).
If her deficits are this severe, then I would recommend you ask your pediatrician for a referral to a neuropsychologist for a full evaluation. I would not recommend having the school do the assessment in this situation, because there may be a neurologically based condition that needs attention. Neuropsychologists have an extra year of training beyond even doctoral level psychologists. Their training includes learning extensively about medical issues that impact learning/thinking/moods. A neuropsychological evaluation will give you comprehensive information about what is wrong and lead you towards appropriate interventions.
Thank you for your help. This information has been most helpful and we will pusue the matter. I will let you know how we get on in the future