R50, not to rouse your Hunesque temperament, but there is no way you can prove descent from Attila, since he was around in the 5th century, and there really isn't much on him published, and there are many claimants to descent from one of his many seed plantings.
Your mother is like many in my family, including my own mother, telling tales of fancy that have been passed down to her, unchecked.
The science of genealogy involves establishing true links to these people, via actual records...and the person above descending three times from Margaret of Scotland, well, you can't rely on other people's family trees, because they are filled with as many fairy tales as a Grimm Brothers library. Documentation is key.
Now, many noble families (including Margaret's House of Wessex and her husband Duncan's House of Dunkeld) have published their established and well proven family lines going down a few generations past famed nobility...so if you can get your hands on the published genealogies (in books, not Ancestry user trees), and then establish, with records, your connection to any of those descendants in the volumes, THEN you can claim descent, and which has been hinted at, one can have multiple links to the same person. Every single one of us has married cousins in our direct ancestral line - the notion of married cousins producing mentally deficient offspring is false more often than true. It's when double cousins marry, as in, a bride and groom who share both sets of grandparents (essentially giving them similar DNA to that of siblings).
Another popular tale I hear in my research is "We descend from a Cherokee Princess!" In fact, every white family who hires me tells me some version of this story. Right, all white people are part Indian. How exotic of you all. *eye roll*
Interestingly, it's quite easy to establish descent from Pocahontas. Many people do, and there are ample records for her. Again, she was famous, so there are plenty of people throughout the last few centuries with access to, and interest in, finding and preserving ancestral records, when it comes to famous people. Again, the trick is to establish your line to one of the known and published descendants. Now, Pocahontas wasn't as far back in history as Margaret of Scotland or Attila the Hun, so keep that in mind as well. Any famous Americans, even early Americans are very well documented.