Ghazi, what problems are you mainly running in to with Rom?
My first playthrough was with a SL4 character (this games nearest to SL1) so I know about one-hit kills from bosses! I'm linking to my SL4 run not to say "I'm a bad ass!", I'm far from the only one to do a SL4 run, but because I played it SUPER, super catious, safe and slow and that's how I killed her at low health after about half a dozen tries. Taking out all the spiders, slowly picking off the stragglers around the edge until it was just her.
Take out at least the first wave of spiders, take out ever last one if you want I think I did and dodge the ice/magic attacks. You can roll dodge them as they come down or just outrun them which I find easier. The little spiders weak point is anything but their heads, which I guess you've already worked out. As always don't get greedy, get a few hits in and then get out before she does an attack. Keep on the move. If you try to keep Rom in the view of the camera even when you're far away you can see which magic attack she is going to do because they all look different.