In theory. But it's highly unlikely that something like that would happen.
In the olden days, when things like that happened, it was because candidates didn't really run against each other.
They each had a block of delegates committed to them show up at the convention and slug it out.
Nowadays, they slug it out in the primaries and the weak ones withdraw early on.
I think she's leaving the door open because if she closes it completely, her audience loses interest in her fast.
Especially contributors to the Clinton Foundation.