A starboard boat headed up towards the line ahead of me — wasn't her course change the foul, not mine?

No. On opposite tacks Rule 10 makes the port-tack boat keep clear, and keeping clear is a test: the starboard boat must be able to sail her course with no need to take avoiding action. Port had the room and the seconds to tack out and spent them hoping. The starboard boat's head-up is fine: Rule 16.1 only asks whether, when she changed course, the other boat still had room to keep clear. A tack was still available, so she did. A course change only breaks 16.1 when it takes the escape away.

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