My daughter thinks that no one loves her

My 7 year old daughter says that no one loves her.  She says that to me and to other kids in school and park.  Everything was fine up until she started 1st grade.  Then her best friend dumped her in the beginning of 1st grade and she did not have anyone to play with for the longest time.  Her ex-best friend would tell other girls not to play with my daughter.  I have another friend in the neighborhood who has 2 daughters.  Even they refused to play with my daughter.  So, the 3 of them get together in school and after school pretty much everyday.  And seeing them together and not being part of the group really hurts my daughter.  I started to go to her school during lunch break and tired to help her make new friends. I though she had started to feel better but I overheard her saying to some girls in the park 2 days ago that she does not have any friends and no one to play with.  Then she asked them if she could play with them.  After a few seconds they were playing fine.  Now she is in 2nd grade.  She is very intelligent, smart, caring loving but sometimes completely ignores me and is impolite.  When I talk to her she apologizes for her behavior.  It seems that she is into her own world.  I do not know what I am doing wrong as a mother.  How can I help my daughter understand that we all love her very much and help her make new good friends?  Please HELP!!!!