I'm thinking of using my neighbor's account without asking.
That's theft! You should ask her first.
I told her I will be using the account and she said she was okay with it.
As long as their is explicit permission, I see no problem with this. You should just make sure that you ask first instead of just telling them.
Sounds good to me, who needs to ask anyway.
But you just said you did ask her. I'm happy that it worked out in the end but you really should ask next time.