It's a HARD choice but I decided to go with Perfect High because she doesn't only give an amazing performance but her physical appearance was slowly transformed throughout the film. At the beginning of the movie she's her normal and healthy gorgeous self but over the course of the film as she gets more into drug addiction her appearance changes. Her skin becomes paler and sickly looking, she has kind of blackish looking circles around her eyes, her hair becomes more grungy and unhealthy looking, and she just looks like a complete mess. That takes really amazing dedication to show her looks slowly evolving throughout the film showing the damage the drugs have done to her looks. She's amazing in all of them, though.

I just chose at random. All of these are absolutely AMAZING performances! If it were up to me, she'd have Emmy nominations for Perfect High (Outstanding Lead Actress in a Miniseries or Movie), You Get Me (Outstanding Lead Actress in a Miniseries or Movie), Famous in Love (Outstanding Lead Actress in a Drama Series), and Scream (Outstanding Guest Actress in a Drama Series). Bella is such a BRILLIANTLY terrific actress.
I haven't seen Shovel Buddies, but I have no doubt she gives an amazing performance in that movie.