If these philosophical conversations had been as deep as you assumed they were, it seems some conflicts would have surfaced long before now - not even on this topic.
I'm going to make a wild guess that this girl has some illusions she's attached to yet that life hasn't forced her to abandon & rethink. For example, I don't think she's yet been a Mother !
There is one good example that tends to shatter the illusion you mentioned of giving "ALL" her time (and emotion) to any one person. Writing as a male, I can vouch for that realization as I'm sure most men could after their relationship with their wife/lover makes that sudden turn on appearance of the first child.
No longer are you the one & only in their life, and as a matter of fact you now find yourself in the back seat in some regards (especially time).
But yet that love that exists between you is unchanged ! It just now may need to morph in how it's expressed. It's no less real, no less important in it's role.
I realize that the statement you made about "all time" was a broad, blanket statement and not to be taken literally and if she even used those words I'm sure she didn't mean it literally. But that in itself I think IS one of the biggest fears AND challenges of navigating multiple relationships of any kind. To attach special significance to it because of intimate relations is unfair but still a valid point to be discussed. Hell - we have to balance that in everything we do - work, play, everything ! It's real but all the same often points back to greed & insecurity. If anyone is in a relationship with someone who requires high amounts of time & coddling, it's not going to be easy anyway. As as much as we might "love" that person, at some level, that philosophical part is unlikely to coincide with the reality of day to day living.
To me, it would be a warning buzzer that this person may want & require more overall energy than you have willingness or ability to provide. It doesn't change the love & respect you have for them - only the practicalities of "expressing" it !