Angela is an artificial intelligence created by two researchers, Ayin and Benjamin, in the image of the late Carmen with the purpose of facilitating the Seed of Light Project. This was achieved using Carmen's brain mapping, which consequentially caused Angela to possess her past memories; despite this, Angela was considered a failure to Ayin, who regarded her coldly and wouldn't so much as look at her. Benjamin was the only one who even remotely showed kindness to Angela, and he taught her about her role and how to run a seemingly endless number of time-loops using the "Script."
What came of these time-loops was a constant cycle of torment for Angela and the sefirot which she oversaw; Angela was forced to facilitate their traumas and suffering or stand by and watch, and any situation wherein she would attempt to assist them would automatically cause the loops to reset. Additionally, Angela's perception of time was altered in a way so as to allow her to efficiently react to certain situations — fixed at a speed 100x slower than the average human being processes time. (This essentially means that she had endured these cycles for a millennia, in her point of view.) The entire process caused Angela to deeply resent Ayin and Lobotomy Corporation as a whole, her festering hatred serving as the catalyst that drove her to seek revenge by halting the Seed of Light Project right at its completion... much to the dismay of the sefirot, who had all worked strenuously and suffered so much to finally reach this point.
Soon after the true ending of Lobotomy Corporation, in which Angela manages to attain a portion of the Light generated in the finale, she transforms the facility into what would become known as the Library. It is at this point that she would become its Director and begin luring in residents of the City with the use of specialized Invitations as the Library's Guests, inevitably to be felled and turned into books to line its shelves. Her goal in doing so is to obtain the "One True Book" that would grant her a human body, and free her from her past and the confines of L Corp — a goal which Angela becomes laser-focused on seeing through, using any means necessary.
Regarding Library of Ruina canon points, it's... a long story (quite literally), more than I can put here. If you are unfamiliar with the scenario or simply need some kind of refresher and would like to read it, you can do so
here or
here. (I also heavily recommend reading
this Steam guide as it goes in-depth into the lore and world of the canon itself.)