Why does my female dog not like other female dogs?

I have a 1 and a half year old Papillon that does not like other female dogs. Whenever I walk her and she sees another female dog she starts to bark at the dog and tries to run at the dog but I have to hold her back with the leash. It looks like she wants to attack the dog. Why does my dog do this? Is it a socialization problem? How do I fix this? She has no problem with male dogs.