Did she forget her past memories or is literally acting like a child? Like she is playing ...

She forgot her past memories. In chapter 2, the FL is told by the water spirit that all her memories of her past last will fade away. So basically she become a child mentally, since she doesn't remember being an adult in her past life anymore

Are u just looking at the drawing or u have bad reading comprehension? It literally mentioned early that her past memory fades away day by day