How do I [26F] explain why I ghosted my friend [25F] without either lying or performing a character assassination?

My friend and I have been "best friends" (her words, never mine) for a few years, but I recently stopped talking to her in September 2018 after she made me angry about something — but the truth is I had been looking for an excuse to distance myself for a long time. I find her (openly) racist, catty, judgmental and just straight up mean about people she doesn't even know. Just to give you a quick idea, here are some brief examples:

-We went on a walking tour together and a woman who was also on it was wearing sandals. Her feet weren't the most perfect, she had some hammertoes and other stuff going on. My friend said (rather loudly as well) "Did you see her feet!?!" to me in a disgusted way.

-She makes fun of girls at work who she doesn't even know, calling them fat/ugly/etc.

-She has straight up said on multiple occasions that she doesn't like Asian people

-She talks shit to me about another of her so-called "best friends". For example, I picked her up from the airport after she went on holiday with her friend and she complained about her the whole way home, including how annoying it was that she didn't want to go anywhere because she probably has an eating disorder and never eats so she's always tired/ill.

Anyway, I came back for my dad's funeral and am staying in the area for a month. I went to the place where she works (and I have worked before) to audition and she was there. I pretended not to see her and managed to avoid running into her directly that night. But today I got a message from her on Instagram saying "Hey what's up? You wanna talk? Im not trying to bother you, it just hurts that my best friend of 7 years [this is a generous estimate honestly; we've only even been speaking regularly for about 4] ghosted me. Would be nice to know why." She has previously messaged me once or twice but then seemed to get the hint that I was avoiding her. I guess that seeing me in person made her want to try reaching out again.

I honestly do not know what to say. I've been avoiding it because this is just so damn awkward and I feel like my reasons for cutting ties would essentially amount to a character assassination if I were to give them. I don't want to tell her "I think you're racist, mean, cynical and unpleasant". But I also don't want to lie... It's tempting to just pin everything on my mental health; I have been going through a lot in my personal life lately and on top of that was recently diagnosed with BPD, so I'm in a lot of therapy and it's honestly exhausting and to say that I've been struggling with/putting most of my focus on my mental health is 100% true. But that's absolutely not the reason I cut her off; I still keep up with my other close friends just fine. If I used that as an excuse it would mostly be to spare her feelings and would kind of feel like a cop out. Plus I'm worried about spreading stigma if I throw my BPD diagnosis in there as supporting evidence (I wouldn't be at all surprised if she talks badly about that to other people about me).

What should I say? My reasons for ditching her are that I find her negative, judgmental, racist and just all around unpleasant. But I would feel bad ever saying that to anyone... The only thing I feel somewhat comfortable explaining is that I don't trust her because frankly she has said many not-so-nice things about her other "best friends" so why would I not expect her to do the same to me. I feel I need to say something not only will I likely run into her again in a situation where we'd be essentially forced to acknowledge each other at work, but this message from her has made me feel bad. I do feel like I'd like to provide her with some closure, I'm just not sure what to say...

TL;DR: How do I explain to someone that I cut contact because I think they're not a nice or good person and I don't feel comfortable being their friend anymore, without hurting their feelings but also without lying?

ETA: I just wanted to say thank you to everyone who has weighed in so far; I have been reading every response and am considering what everyone has said carefully as I've gotten some advice from both sides of the spectrum (from telling her exactly why to stick to being diplomatic to not responding at all). I really appreciate everyone's input!

Submitted April 29, 2019 at 11:58AM by wannabepopchic http://bit.ly/2UPA0rA