can you help me find this fantasy book, been looking for it for years

the main character was a woman in a world with super powers, she lived in a school with a barrier, she has the rare power to kill people or creatures with a thought, she uses imaginary purple lasers to control powers, apple also gave to book away free virtually on e books i don't remember the year but its was between 2017-2019 it was strictly a mental image, it was in a real world setting and the first time she used her power was when 2 men were attempting to rape her best friend she also stabbed herself in the second half of the book and i believe angels were also involved in the book the main characters power is to kill people with her mind without touching them she stabbed herself to not be captured because the enemies couldn't touch the knife, it was also the first book in the series it was used as a mental image to control her powers and she had her childhood memories of her powers erased, she first used the mental imagery in a field to kill insects