Mary's baptism certificate lists her as "Marytje Lisjer" and her parents as Hendrik and Anaatje Lisjer", but the baptisms of Mary's children list her maiden name as "Maria Letcher". I expect the spelling changed as it got farther away from the old Dutch family. I suspect Lampman may be a different Mary, who also married a Henry Young... there are at least 3 Henry Youngs in and around Albany at that time, not quite as bad a "John Smith" but almost!
The Prince Edward County UEL chapter has someone how knows a lot about the various Young branches and how they may have been mixed up - Brain Tackaberry has written on it.
As for Mary Barret Dyer - yes, she is an ancestor of the Dyers who married into the Young family.