One shouldn't mix business and personal matters. You just did your job as it was dictated, your friend should have done the same if she wanted to keep her job. Your friend should understand, if she doesn't you need a better one.. Again, you just did your job and you shouldn't feel guilty about doing your job right..
Okay, here's the thing.. No-one gets sacked over a single report unless its something huge.. If a single report from a new hire is enough to get someone's contract terminated, especially someone who worked there for 5 years already, there must be priors and opinions that you might know nothing about.. I doubt its something you should lose your sleep over. Also, first time is always the hardest, if you plan to stick to your job its a good experience else you should reconsider your job profile.
Recently, i just got a job btw, i graduated accountancy and got in into a big company. I got close to.the people but since I got in as an accountant I got to.do.my job which is.to.audit my coworkers and eventually I found an anomally which is one of my close friend. Since this is.my first job i did try to skip/let it go.but my manager found it. She asked me for my report which is my report with findings. Eventually, that close friend of mine is on the process of having her contract being terminated bcs of my report. All the evidrnce presented has my name on it. I feel awful bcs I couldn't say it to her brfore hand to make her be prepared for it. I feel.really bad right now bcs she's so close to me. I feel like i did something wrong, i should've warbed her something but during that time i can't bring myself to her and tell her that she is being audited since it is confidential thing. I am so sad right now and i can't sleep.due to guilt. Huhuhuhuhuhuhu I just can't.