Let me just start off by saying that I absolutely LOVE this horse. She is so much fun to run..when things go right. 

Problem is, I've been running more free runner, large pocket type horses for a long time. This mare is 14.1, and rolls back super hard at the 1st. Literally plants that inside leg and pivots. She isn't as bad at 2nd, we might pull it on the way out sometimes but I feel I can handle that. It's the 1st barrel I'm struggling with. Finding that perfect amount of pocket and spot has been difficult. Too much pocket and she will turn right back into it, literally having to jump over the barrel. When she commits to turn, she's turning..the harder she runs to it, the harder she'll turn.. it's like if the barrel was 3 foot back we'd have made a beautiful turn. Not enough pocket and were hitting it on the way in. 

How would you suggest going about this? There's no changing her style at this point and honestly I don't feel I need or want too, I just need to figure out how "I" need to ride her. 

Instead of thinking about how much pocket, focus on your line to the first.  With roll back style horses, they don't need as much pocket.  They ned a clean straight shot to a specific spot where they can sit and shape for their turn.  Try lining your mare up with a straighter approach to the first barrel, aiming for a point just to the outside of where you'd normally initiate your turn.  This should help keep you from over pocketing and will let your mare snap around the barrel without hitting it.  Instead of sitting down right at the barrel, keep your seat light just a split second longer and then sit and shape her with your inside leg and rein.  During slow work you can do drills where you're riding past your normal spot to help her not anticipate the turn.

I've read and reread this a 100 times and tried to draw out what you mean but I'm just not getting it :( 

Do you mean more like thw middle picture here? Straighter to the barrel, not making a large arch giving a large pocket but actually to a spot on the back back side of the barrel? 

Pick me! Pick me! ALWAYS pick yourself a visual point somewhere outside the arena. Train your eyes to look up not down at dirt. NEVER think about turning. When you feel the first hint of rate, use your seat to ask for another step. Once you master it, you'll fall in love with the roll back style.