Hey Noski. This happened to me with the closest friend I ever had, and I eventually found out it was partly because she felt smothered by me, but also partly because her life changed when she moved to NYC and was busier than me and more fulfilled... We were friends in person for years, but long distance it really suffered, and I haven't heard from her now in months, the last time being when she was asking that I give back some of her things.
She ignored my calls and messages for over a month before deciding to tell me that she was screening my calls (when after agonizing I convinced myself she was too busy to text me.) So, I definitely feel your pain.
Actually, I think it will give you closure to email her and ask. If she doesn't respond, don't wait for her, unfriend, unfollow etc... It struck me that it's possible she wasn't who she claimed to be since this was online... That could be a reason for her cutting you off. However, if you email her, it'll give her a chance to explain herself that's easy and not too high stress.