Why can't Atticus pity Mayella?

I may not be correct but Scout learns from Atticus from the start of the book till the trial to judge others fairly and that if she wants to understand someone thoroughly she has to 'climb into other people's skin and walk around with it'. She does this to Mayella and finds out that Mayella is a lonely girl. She has no friends as she is too poor to mix with the whites but can't mix with the blacks because she is a white, therefore when Tom Robinson treats her well she thinks he likes her therefore lost her mind when she tried to kiss him. Hope I answered your question!