I don't think anyone but your friend can figure out her sexual indentity, she has to figure out for herself but what you can do is talk to her and ask her if she is attracted to the same sex and tell her if she is she has to do what makes her happy and not what makes everyone around her happy and that you support her no matter what her sexual orientation is. If she does come out as being gay don't desert her stay close to her and show her that you love and support her no matter what and unconditionally, she may have been waiting for someone to tell her it's okay. Sometime people that struggle with they sexual identity feel alone because they feel as though they may lose friend if they come out as being gay or liking the same sex. Also reassure her if she does come out that she can still have children through other means.
If she denies being gay then tell her that if she ever needs to talk to you, you will be there for her no matter what it is, she may not be ready to be honest with herself let alone anyone else but at least you opened that door. The only person that can help her figure out what she wants in a mate is her don't pressure her or it will make her shut down even more because people that are struggling with the sexual orientation are usually ashame to come out because the way society looks down on them and it could take one good friend to make them realize that all they need is one person to understand what they are going through and it makes it easier so just be her ear when she needs you to be.
I thought you might say something like that. I know it's a journey of self-awareness but my concern is that I may offend her, and she's getting too old to not know by now/be in denial. This is something that all of us close to her have struggled with, do we say something or not? And, truthfully, I don't even know if she has lesbian tendencies... at this point, I would call her asexual. I think either way, gay or straight, she is uncomfortable with that aspect of herself. And, she's even said that if she's still single by the time she's 35, that she'll get A.I. Yet, as one of her closest friends, I feel it's almost my duty to help her down the path of self-discovery because after spending a few days with her on a trip to Chicago last week, I realized how critical of others, and negative she's become.
Thanks again for your insight, I appreciate it!
As a friend we always want to save our friends and you want the best for her so tell her that before you ask but definitely ask her to be honest with you and herself and ask her could it be that she is sexually attracted to women and is afraid that people would judge her. If she finally figures out what it is she wants she may become a more pleasant person I think she is frustrated and that frustration has made her negative and lonely and sad. There has to be a reason why she hasn't had a long term relationship and if she discovers who she really is then she can be completely happy within herself and her life.