Do you mean you've only put 5 rides on her or do you mean she's only ever had 5 rides total in her life? Because that's not very much.
If you don't have your horses head you don't have much. They need to be soft in the face, to give to the bit, to collect and that takes some time. Until you get that they'll just blow right through their shoulder.
I know a grand total of zero about barrel racing, and this is free advice so take it for what it's worth
but a good exercise for a horse is to start by walking along a high fence at a steady rate. Pick up your direct rein (fence side in this case) and slowly turn her head towards the fence. The instant she commits to the turn release the rein and let her finish it on her own and then continue down the fence in your new direction. If you keep doing this you will get to release earlier and earlier in the turn and she will also develop a nice roll back. As she gets it you can pick up the pace.
Don't know if this helps for barrels or not but it's a good foundation exercise.