In your case, Marlys is likely an anglicisation of the Dutch/German names
Marlies and
Marlis, especially if the pronunciation is virtually the same (though the stress may be placed differently in English).
The aforementioned names are currently also in use in Scandinavia, though they are rare there:
•
Marlies:
https://www.nordicnames.de/wiki/Marlies (in English)
•
Marlis:
https://www.nordicnames.de/wiki/Marlis (in English)
Also, I'm from the Netherlands. :) I checked whether Marlys is also used here and in Flanders (the Dutch-speaking part of neighbouring Belgium), and it turns out that it is! It is extremely rare, however:
• Belgium:
http://www.names.be/meisjesnamen.html?met=Marlys&sort=beldesc (in
Dutch; shows the prevalence of the name in 2009)
• Netherlands:
https://www.meertens.knaw.nl/nvb/naam/is/Marlys (in
Dutch; shows the prevalence of the name in 2017)
Marlys would be pronounced the same as
Marlies here. I also think that the average
Dutch person would be inclined to see Marlys as a creative but unusual spelling of
Marlies. They would describe it as:
"Marlies, but with a Greek [letter] 'y'."
Lastly, one of my maternal grandmother's sisters happens to be named
Marlis. She (as does the rest of our family, of course) pronounces her name as mahr-LIS. As you can see, the -ee- sound (that is present in
Marlies) is absent there. It could be that that pronunciation is just specific to her, as it is technically possible that (at least a few) other
Dutch women with the name pronounce it as mahr-LEES instead. I guess you could say that it is one of those names where the spelling is ambiguous enough that its pronunciation will depend on the bearer... on how their parents taught them how their name is supposed to be pronounced.
"Great minds discuss ideas; average minds discuss events; small minds discuss people."