Seemed like the invert of a certain famous animated movie's finale.
Pieta finally comes to the realization that what she'd consider happy memories, thoughts and moments can also have a sad side to them, yet instead of being consumed by them like the other Pieta, our protagonist accepts that both things can coexist at the same time.
I don't know how much her father's death was a part of this, but it definitely was one happy moment that had her anguished for a long time, as she probably struggled to understand it at the time (she was younger) and refused to look back on it, maybe coming to terms with this made the other Pieta become despair filled.
In the end she finishes her painting, it is not happy nor sad, but abstract, probably showing that she managed to correctly put her state of mind on the canvas, letting her finally overcome her self-imposed trial.
Thoughts? Think something I said is right, think something I said is incorrect?
Really liked the end of this arc, I wonder if there'll be another part to it.