You do need to be very careful here or you risk driving her away when she gets older, or (worse) making her so worried about your feelings that she is afraid to start her own adult life when the day comes.
As an adult now, your response should be a cheerful "that doesn't matter, I love you and always will do". Don't encourage these conversations, never ask her who she loves most, but if she does bring it up, just reassure her that loving people is absolutely fine and not something you have to worry about. Let her sense rather than hear that your love is unwavering and that you are strong enough for both of you.
Thomlin put it extremely well: "the only thing that really matters is that I'd die myself to keep her safe, wether that feeling is returned doesn't really matter"
She is not there to make you feel good about yourself, that is too much to lay on a child. You need to model independent and resilient adulthood so that she eventually feels secure enough to grow up into an independent and resilient adult herself. And if you don't feel it, then you fake it.
And try not to let your own thoughts dwell on the sacrifices you have made in the ordinary care of your child. You chose to have her, so you chose to do that work, she did not choose, she is not the one who has to feel grateful. She probably will, anyway, one day, because most children do, but it will be an awful lot easier for her to feel that gratitude if she doesn't sense that you are thinking about it.