I also have an OTTB. She is better to the left (from racing) i also did not have a round pen. I do a lot of ground work like bending or making her move her haunches and shoulders I do a lot of pole work to keep her mind busy. For my OTTB she gets bored easily and likes things to be her choice. The louder I get the "louder" she gets so it took a while for her to learn that I heard her and I wasn't going to react when she did; I was just going to redirect. Also I start her on the right on the lunge line because it will take more effort and strength and then the left is her confidence boost to end on. Hope this helps/makes sense.
You might want to put a chain over her nose one time if she pulls you. I had to do that with my guy since I'm not strong enough to pull his head back around.
If possible, turn her loose in the arena and free lunge her. My horse is so lazy on a line and I have no real way to "chase" him and get him going. The arena gives me that freedom.
Get your hands on the establishing respect and control book by Clinton Anderson. I'm not a huge fan of Clinton, but it's a good book. I altered some of the book with more methods from Warwick Schiller. Worked nicely.
Liberty work! It's made my horses so much better and they respect me hundred times more☺️
You could try join up with her. It helps horses to trust and respect you. Monty Roberts came up with the process.
By mostly trained, I mean she is fairly good with transitions but still pulls on the line - especially to the right.