Her back is a bit long, which can make it a bit weaker especially since her underline is fairly strait and her belly is a bit thin looking. She does not look like she has much abdominal muscle to help her support her back.
For barrels, I would want to see her hip a bit stronger. She does have good deep hocks, which will help her dig in.
If you are undecided about what to do with her and have an idea that you want her to be an all around, I would just work on fine tuning her handle. You can do a lot of work just teaching to her to take detailed direction from you and 3 is still pretty young. If you keep working on the basics, there is no reason you can't do all that you want to with her.
A horse that has learned to take direction from their rider can go into any class and perform well.