Well, it made me quit, because I once almost defeated he, but I died. I never came close to doing it after.
All about timing. If able, I try and stay near one of those platforms at all times. That way, you can dodge her tentacle attacks. After that its just about doing as much damage as quick as you can to each tentacle "pylon" to whittle her down.
And for those, you can just wait for the arrow to appear to show you where they are, dodge her left/right attacks as needed as you make your way towards it.