From what I know based on research from Johnstone's "Heraldry of the Douglases...", the Douglas of Drumlanrig COA was most likely the same as the 2nd Earl of Douglas...
"1 and 4. Argent, a heart crowned gules, on a chief azure three stars of the first. 2 and 3. Azure, a bend between six cross crosslets fitchy or."
Most likely, the Drumlanrig COA was as above with an engrailed red border (unproven). This was certainly the case by the time of James, 7th of Drumlanrig. I will see if I can recreate something for you.
The more information you can give about the people you mention, the more chance there is of someone else connecting with your family.
Dates and places of births, deaths and marriages all help to place families.
Professions also help.
'My great-grandmother mother was a Douglas from Montrose' does not give many clues to follow up! But a bit of flesh on the bones makes further research possible. But if we are told who she married, what his profession was and where the children were baptised, then we can get to work.
Maybe it is time to update the information in your profile?