I really like Elsa and love Anna. Your art style is beautiful and has a natural professional oil painting feel despite it being digital. The style also fits the characters and the surroundings well.
I love Anna personalty and traits of optimism, fun, adorkable, and feistyness. I enjoy seeing works and fiction with Anna having powers. Many give Anna fire and association with Summer due to the opposite nature of Ice and Winter which Elsa represents and controls/embodies due also how their personalities differ yet round each other out. But many also associated Anna with Spring out of all the seasons (especially if Merida/Fall and Rapunzel/Summer is included) as well and Anna favorite color is green and wears something green throughout the film on her outfits plus the joys and embodiment of life she portrays. Thus Spring is Plant/earth/flower related as majority of plantlife bloom in that season. Though there are certain flowers and plants that bloom in the other seasons such as the Arendelle's crest the flower named Crocus. The Crocus is a symbol of rebirth and spring. In cold regions, the flower blooms while snow is still on the ground).
Perhaps like in the movie Anna had fun playing with her big sister Elsa growing big and funny looking trees they would climb on, wooden slides, and wide fields that from the sky one can see colorful works of nature art. On day was enjoying a chocolate picnic made with cocco nuts from Anna on top tree Anna grew under them and looking at the beautiful colorful flower garden kingdom, hedge animal creations and mazes, Strawman, and nature Anna made below all for Elsa. Elsa however slipped off the branch and Anna frightened tried to create a plant to catch her softly but hit Elsa instead in the eye. Elsa landed with a thud and didn't awaken but moaned alot. From the eye a small plant grew and slowly rots began to creep under Elsa's skin. Anna horrified called out to their parents while clutching Elsa. Elsa was taken to some mysterious trolls whom was able to save her from death but not the eye. Elsa's memories was taken away so she would not remember the pain or the event as the parents feared it could traumatizes her and have her fear the sister. But Anna remembered and the fear and guilt took a toll on her mind and powers. Roses thorns grew large and sharp, fields withered and produced uneatable fruit and vegetables, animals couldn't find fields to eat, and plantlife became unpredictable and thorn bushes, damaging trees, and vines grew large. Anna for the safety of herself and others was placed in a newly built tower far from the earth below and others. Anna was given many things to play with and special tutors and servants to assist only her but had to stay in the tower high above at all times intill she was able to control her powers. As she grew so did her powers. Looking down at the kingdom watching life and joy go on below she longed to return to the people and earth but feared it at the same time. She feared most of all to hurt her beloved sister again the heir to the throne.
Elsa however didn't know what became of Anna nor recall her powers. When asked she was told Anna had developed a grave illness and was put into special care for protection. Elsa could only talk to Anna by messages hoping she would get well soon while Anna responded with words and pictures of art that she practiced and became natural during her time in her tower and watch Elsa secretly from above. Anna furthered did anything to entertain herself and passing the time such as talking to her favorite paintings that was moved to her tower particularly Joan.
The parents understanding it was Anna's emotional turmoil that was causing the magical problems and the situation wasn't advancing to where they had hoped for the daughters made "special" metallic gloves and boots telling her that they were magical and would block her magic. As extra precautions a wheelchair was also made for Anna so her body would never fully touched the earth. Anna believed her parents using the gloves and boots like a magical crutch never wanting to take them off nor go anywhere outside without the chair dispute able to run marathons secretly in the castle but was antsy to go out once more.
On the day Elsa was to become Queen Anna the new heir was royally obligated to present Elsa with three symbols of Arendelle and the royal family during the coronation. Elsa was posed but underneath was thrilled to see and be by her sister again. Anna had mixed feelings as for the first time in forever she would be part of something and apart of the life, fun, and celebrations the kingdom held and be there at her sister side during her special day but her natural exuberance was tempered as it also meant removing her gloves during the coronation to present the scepter, orb, and the flower Crocus to Elsa.
I'm going to stop typing here as I have to handle other things but I can see Anna making and having a palace made entirely by plants/nature. Her dress made of flowers, large petals, and small vines and a very small flowers in her hair like the snowflakes Elsa had. Unlike Elsa whom we didn't know how she would eat and survive in her castle in Anna's Nature/Flower Palace a garden that's fully editable and Cocoa trees providing her with chocolate that she makes from them. Also f
eeling good with some shrooms being a bit of a hippy