First, I have to say how impressed I am 1) that your daughter is able to know how she feels about the attention she gets from boys and is able to say that she doesn't want or appreciate it (even if more to her friends than to you) and 2) that you are such a caring father you are seeking more information from others. I value humans who are humble enough to look for help when they know they need it. Namaste! Many girls in our American culture 'dress to impress' and are looking to get much attention from boys... and of course most of this attention is based on how they look. I believe it makes the girls feel 'worthy' 'valuable' 'special'. The fact that your daughter does not cave into this and can feel good about herself without desiring the extrinsic accolades is to be congratulated!
I am also very impressed with your daughter for understanding the kind of attention the boys seem be giving which may be more superficial versus the attention that she gets from you, which is heartfelt and compassionate. Good for her!
I personally believe that having her kiss you on the lips is a display of her complete and utter trust in you. It is the highest compliment. I understand that it made you feel uncomfortable. My husband also does not like it when our children (I have a 15 year old daughter) try to kiss him on the lips... He prefers the top of the head or the cheek.
I think it's important to understand WHY you feel that way. It comes down to your perspective. My husband associates lip kissing with more of an intimate (and sexual) act. For him lip kisses are reserved only for romantic relationships.
I, however, was raised in a very affectionate family... Both my mother and father would kiss my brother and I on the lips. At 47 I still do. It is a peck on the lips and only lasts a second. To my family, it is considered normal. Our children have had both modeled... They have learned "Dad doesn't like that" and "Mom thinks it's fine"... Sometimes my children will kiss me on the lips (I have five children ranging in age from 17 to 9 ... all boys and the one girl)... Sometimes they put their cheek forward for me (Usually when we are in front of non-family members)...
We honor both ways of doing things. The few times I've talked about it alone with my kids, they have sort of asked "What's wrong with it?" and "Why is Daddy uncomfortable kissing me?"... like they get the impression there is something wrong with him or something about kissing on the lips might be wrong. I've explained that we all have our own comfort levels and there is no 'right' or 'wrong' ... just 'individual' and it's important to be honest with others about your level of comfort and it's equally important to honor what others need to feel comfortable. That means that each and every relationship has it's own boundaries, of necessity, to accommodate individuality.
I am a LITTLE surprised your daughter would kiss you on the lips if this has not been part of your history and if it has never been modeled... but again, I believe it is her way of showing you explicitly, the level of trust she has in you. It makes my heart very happy for you!
In regards to her feelings about other boys in general... My own children are also exploring their feelings about the different genders. My daughter has told me she feels she may be "asexual"... in that she feels completely uncomfortable with the idea of anyone touching her or kissing her. I believe that will change as she gets older, but I've made sure she knows that no matter what, her feelings aren't 'wrong'.. and wherever she lands with a relationship (or non-relationship) will be fine with me.
My daughter's best friend, who is 16, has had similar reactions to boys as you describe for your daughter. She doesn't like boys at all. Ultimately, she now has a girl friend and defines herself as lesbian. She gets support with this identity from her mother, but not from her father. She visits us regularly and I can see how hard it is for her to know that her father can't accept her sexuality. I do my best to let her know that when the time comes she will be able to embed herself in a community that is fully supportive.
I know for myself, I would hate for that community to EVER not include me for my children, so I have made it clear to them that no matter what... they will be loved and accepted.
NONE of this is to say that I think your daughter may be gay or asexual or anything... Just that there are MANY possibilities and you may never know unless you find a way to broach the topic with her directly. I believe that NOT talking about topics with our kids... by the very absence of it.. it sends a message that the topic is 'bad' or 'inappropriate' or 'wrong'... In reality, it's just part of human nature and every human has a sexuality... whether they talk about it or not.
I would ask you to look inwardly to yourself and find out how you might feel if your daughter doesn't end up liking boys ever... would you be ok with that? What are your ultimate hopes for her? Is it ok with you if your vision of what would be acceptable is not what would make your daughter happy? Also, consider that just by saying to her that she needs to develop relationships more with the boys at school... She MIGHT interpret that as your way of saying there is something wrong with her... so please consider the message it can send to her.
I like the answer that Meg gave above, describing that she was behind her peers and didn't like boys until College. I believe that each person is unique and they should follow what feels authentic and 'right'... I'm guessing that you would ultimately prefer for your daughter to begin to like boys on her own accord rather than to do so superficially just to please you? If so, consider accepting this for now the way it is without feeling the need to 'fix' it.
Truly... to me she sounds like a girl who is putting her priorities in the right order right now... and she's being true to herself. She can't have gotten there without great modeling from you :)