There's a lot of assuming going on inthis thread.
Yes, she may have just been a rubbish friend who failed you, OP. Or something could have been going on in her life that she found difficult and she didn't have capacity for anything else.
I had a good friend cut me off last year. She was going through a terrible time with her MH and physical health, and I'd been a supportive friend for a long time. I didn't contact her for 3 weeks in July. She didn't contact me, either. When I got back in touch she left me on read. This happened every week, then every fortnight, then I stopped trying. I'm pretty sure it's because she was upset for me not being in touch those 3 weeks, although she could have messaged herself.
What she doesn't know is that the reason for me going quiet is that my dad, when in hospital on morphine, wanted to talk about things from my childhood. There was physical, emotional, and sexual abuse in my childhood, and as much as I've dealt with it through therapy and am generally pretty stable and happy, very occasionally, something comes out of nowhere and it all comes back and I've got to work through some very complicated thoughts and feelings. When that happens I withdraw from people until I'm more settled. I'd have been able to explain this to her if she'd just engaged with me.