How to end a friendship?

Should it be in person, text, phone call, ghost her?

What I thought was an otherwise good friendship with someone, signs are pointing towards her not putting ANY effort into keeping it going.

A little backstory: She is my recent manager and she lagged for months, since last October, to write me an LOR. She waited till almost the very last day after dodging some of my texts. The school even extended the deadline for me and she still “couldn’t get the link to work,” even though they said it showed she logged in and didn’t answer any of the questions when she uploaded her LOR document.

She never checked up on my application. It’s for my MASTERS FFS. She knows how difficult my journey has been and I feel like I gave away my power when I said “that submission is the only thing holding my application back.” I just don’t understand how a friend would not be more diligent and thoughtful in such an important situation. I gave her a straight up way out, and I said if she just couldn’t get it done that I would ask someone else and she insisted that she would do it for me. I just don’t get it.

She had already stopped sending me memes and hasn’t added me on IG after I left work beginning of January. She was so happy to be full friendship status because I am no longer her employee.

She knows how much I appreciate her and care for her and love her, and I have shown acts of all these qualities. She knows how excited I am to finally have her as a full-fledged friend. I just don’t understand why she doesn’t have a problem letting me down. This isn’t the first time, either.

Tl’dr: I seemed to have misjudged a friend to care for me as I do her. She let me down in a critical way and maybe ghosting me, (side note: she had literally told me that she can be so ashamed for doing something stupid or wrong that the easiest way is to ghost). How do I respond?