Complex sentence: Jessamy, however, found the envelope tucked down the side of the pram, opened it and took out the note, but was seen by Mrs Stubbins, who chased hers, so that she was unable to read it.
Split into simpler sentences: Jessamy, however, found the envelope tucked down the side of the pram, opened it and took out the note. She was seen doing this by Mrs Stubbins, who chased her, so that she was unable to read it.