I'm going to cut off an online friend
Why are you cutting off this one specific friend?
Well, she's a user. She doesn't appreciate my help
I'm sorry you're fed up with her, but maybe you should stay with her a little longer. Like you said she has so many problems going on, maybe she's just too overwhelmed that she forgets to say the most basic things. If you leave her she will get worse and it may be all your fault.
She knows I'm a busy person but you don't cut people off for being busy.
Then be honest with her, if she is using her tell her that and let her know it won't be tolerated anymore if she wants to stay friends.