Help me out

I recently got into one of those pointless arguments couples normally get into every once in a while:

Her: My hair is a mess.
Me: That's because you forgot all your stuff (hair care products)
Her: I only forgot my hair dryer!
Me: Yeah, your hair dryer is "all" your stuff.
Her: No, "all" means "a lot of things". I just forgot one: my hair dryer.
Me: But is that the only thing you needed?
Her: Yes.
Me: Then its "all" your stuff. "All" may mean "many things" but not necessarily so. It can also mean just "one thing" as long as that "one thing" is all you need.
Her: It does not. "All" means "a lot". It can't mean "just one thing".
Me: All can mean "just one thing".
Her: It does not.
Me: Yes, it does.
Her: No.
Me: Yes.
Her: * Pffft *

Help me out: does "all" have to mean "a lot of stuff"?