Nella's bow is the transformed state of her sword. She can toss it up into the air and it will change shape without requiring verbal instruction, likely meaning it is triggered by thought.
She tends to fire ribbon arrows to impede enemy movement or to rescue people from falls/crashes.
Her bow is unusual in that it has a projected purple handle to grip, rather than simply holding onto the pink portion (handle riser section) which connects the green upper limb to the green lower limb.
This likely aids in allowing her to draw the string further than she otherwise could due to arm shortness, however it could also make the bow less stable to aim, requiring a strong grip in the non-drawing arm to keep the handle and Arrow Rest / Sight Window parallel (lined up to target) and not twist left or right.