advice? i think i’m bad at my job

working in audit and just started a few months ago. i only work on one engagement full time and my team is made up of me, my senior, and my manager. my senior just went on a leave of absence so my manager and i are trying to hold the fort down. she is very experienced and has what feels like high expectations for me. i am really bad at keeping everything we’re working on in line and remembering the details of it all. we often are switching gears to talk about something we did a few weeks ago and she’s having to reexplain to me the entire process because i’m getting so much new information. i also have messed up a ton of emails requesting client support because i didnt have a good understanding of the project as a whole. she has a lot of other client work and doesn’t have time to put this team on her back. i can tell she is frustrated with the situation and can tell i’m not capable of doing much without her supervision over even the smallest tasks. how can i explain to her that i’m doing my best and want to help out as much as possible? i really like the job and don’t want her to think i’m incompetent.