It's sad she couldn't /wouldn't be more upfront as to her time & energies before it got to the all or nothing stage.
Maybe for some reason the friendship, time, internet came down to a choice for her and she had to make that choice...

Something in her life must have changed or caused her to make a change - who really knows - and maybe in time she will contact you and explain more.
Some people get kind of addicted to IM friends and at some point they have to stop cold turkey..