Complex sentence: Lucy arranges for "L Stevens" to visit Mandy not realising "L" actually stands for Lorraine, Mandy's estranged alcoholic mother whom she has been providing with money.
Split into simpler sentences: Lucy arranges for "L Stevens" to visit Mandy. However, "L" actually stands for Lorraine, Mandy's estranged alcoholic mother whom Mandy has been providing with money.