Dodgy msn person?

ok so sumone added my friend on msn. my friend has never given away her addy and she didnt know her. but she still added her stupid i know.anyway this person is a 20 year old lesbein who keeps on trying to asking my friend so my friend can see her (the 20 yr old lesbien) when she is getting dressed. she also keeps on trying to give her 'pictures' my friend is only 13 and the 20yr old girl wont tell her where she got her addy from. my friend wont report it as she doesnt want to go thru all the legal stuff and what happens if it just a mate playing a trick. what should i do