I can see how she tosses the word "love" around. Grown-ups do it all the time: "Oh, I love that song!"; "I love Chinese food!"; "Don't you just love these shoes!"; "I love my new car!".
Seriously--sit and keep track of how many times you hear or see the word "love" in one day.
Your daughter doesn't understand "love", but adults use words they don't understand--or don't understand fully-- all the time.
If this were my kid, I would ignore it for now. She is awfully young and probably just starting to get in on the boy/girl dynamics. I highly doubt she will be using this word next year. She's not capable of fully understanding love, and she's also not capable of fully understanding marriage, for that matter, either. I have heard young children say they want to marry their mommy or their daddy, because they love them. She is just starting to grasp this stuff--she will understand it more in her own time. Let her be a silly 6 year old.