Phonemes

I post this question here with hope that someone could help. Recently I''ve got involved in helping somebody to pronounce a few English words - I''m not perfect myself, but since she could not find anybody else, she approached me. I could decline of course but I felt it''s not very nice to do so. She has a serious problem in recognising and pronoucing correctly words with syllables begining with "N". She pronounced it as a "L", and thus "SNOW" became "SLOW", "MORNING" became "MORLING", even the Vietnamese "HANOI" became "HALOI", "CON NAI" (VÀNG) became "CON LAI" (VÀNG) - (ie. con lai tây). Apparently, she did not have this problem when she was still living in Hanoi. Now that she''s living with a group of people from Haiphong, who has this problem, she''s managed to copy and "adapted" to this habit.
I thought up several ways of helping her to hear what she was saying, with hope to help her to identify the wrong sounds that she is making, but they all seems helpless, and so am I. If you have experienced in correcting someone with similar symptom or found a website where helps to this particular problem is addressed then please feel free to post the link or help with your advices. Please receive my sincere thanks in advance.