I will admit, I don't use the "before/after sequence" much.. so you should definitely test this to make sure what is returned is expected data....
But I think you can do this with containers....
The entire segment is a "Visit" level definition, then I placed the A > B sequence in a container (also Visit Level), and applied a "Only After Sequence" to the container.
Following the Container, I added Page C.

If you want the flow to be consecutive, you can use "Then within 1 Page View", instead of just "Then"
IF you just want the hits of Page C... then you can change the Segment to "hit" level.. leave the container as is (Visit level and After Sequence) but change your Page C to "AND"

This will look for Visits that have the sequence A > B, that also hit C (but C has to come after the A > B flow), and will restrict the returned data to just the hits on Page C (that meet the criteria)