My two close friends are ISFJ and ISTJ and it took me a long time to figure out that L is ISTJ, not ISFJ. The biggest difference is that the ISTJ female cannot for the life of her tolerate most girls our age. She thinks they are stupid, unethical and silly. She doesn't like girls dancing on tables or singing from balconies. She will never make a fool of herself. Or go out of her way to help a stranger or acquaintance. She is warm to those she is very close to, but only those people. She has a hard time letting people in and trying new things. She minds her own business, likes social commentary like I do and only recently began to be more 'girly' and 'feminine'. She always have a solemn expression on her face and for those who don't know her, she is quiet and serious, but once you know her, she is goofy and silly. I won't say she is masculine, but she is aloof and down-to-earth and not a chit-chat, girl bonding kind of person.
My ISFJ female friend is much, much more people oriented. She loves to help people and have conversations with strangers. She tolerates the other girls and accepts them, huge flaws and all. She is very giving, generous and sweet and not just to close friends. She talks about her life, gives personal details willingly even to acquaintances. She is good with people and always makes them feel welcomed and appreciated. She gives compliments frequently. A lot more emotionally expressive whereas the ISTJ is very toned down and does not show vulnerable or needy side. She is very much the chit-chat, girl bonding type.
I can expand more if you want more details. I just love these two friends of mine.