I think that the first thing that you have to do is to initially compile a list of male surnames connected with that side of the family (the Aunt's) going back, at least, to the 18th century. From this list you will have a base from which to work and you should then examine the arms registered in those surnames and eliminate those that do not have arms recorded against that surname.
To do this you will have to get a genuine paternal pedigree for the Aunt's side of the family done dating back to the 1700s. If she was married, this would also include the husband's paternal pedigree.
Had the arms been of British origin, the task would have been much easier with the use of an 'ordinary of arms' (like 'Papworth's) to hone in on the actual design. Unfortunately, I don't have the resources to enable this to be done with non-British (Continental) arms.
If/when you have that paternal pedigree of the Aunt's side of the family, perhaps you could share those surnames with us and we'll see what we can find for you.
If the arms shown follow the accepted hatchings for heraldic colours I think that the background of the shield would be red (Gules - vertical stripes) and from that fact the Roses should be either gold (Or) or silver (Argent).