Interesting, Matthew, but a privateer surely couldn't be anything like a ship of the line. A clue here is that she ran from a French 44.
If as Rahere said she would have been at least a 50 she wouldn't have been running from a French 44.

However we have to take account that many maritime ballads in particular were rewritten several times over and that's without even taking oral tradition into account. One ploy by the amateur poets was to take an existing ballad from a previous era and simply change the name of the ship and/or a placename and sell it on to the printer. If Matthew's privateer had been in the news lately the poet wouldn't be too fussy about the size of the vessel and its compliment.

An excellent example of this process is HMS Nottingham > Wasp > Lion > London > Dolphin (Roud 690) not necessarily in chronological order. There are plenty of other similar examples.