Do you have any idea why this has happened? Whether you see it as a proportionate response or not?
I have adult children, and can't imagine a circumstance where I would ghost either of them, but that's really not my style with anyone. Have you asked her what the problem is? I never find that second-guessing other people is helpful.
If she won't talk to you in person, maybe send her a text on the lines of 'Mum - I don't know what's going on with you, and I won't unless you tell me, so this is not going to get better. I'd rather we talked than texted, but I'll wait for you to reply to see how to move forward.' Basically, acknowledging that you are aware of what she's doing, but not accepting that there is a reason for it, whilst being open to a discussion that might improve things.
I'm second-guessing now, but if your mum was brought up to avoid conflict, she might not know how to deal with things other than with silent treatment. That's not to excuse it, but it might explain it?