In the audio file, it doesn't seem like either word is being stressed over the other one.
However, when multiple adjectives are used, there is an order in which they normally occur. Adjectives based on your own opinion tend to come first, followed by descriptions of size, and then physical qualities.
Based on this, I would say that as the adjective of "scary" seems to have been demoted from a matter of opinion to a matter of fact, it is the person's size that is being emphasised. If the size wasn't important, they would have just said "a scary lady", but this is a big scary lady.
I will add though, that there is a difference between how British and American English speakers might say "scary lady". It could be intended as a compound noun, like "rocking chair". With compound nouns, Americans have a tendency to put emphasis on the first syllable of the first word, whereas British speakers tend to put emphasis on the first syllable of the second word. For example:
American: Robin Hood.
British: Robin Hood.
This can lead to the final adjective sound like it is part of the noun, and any additional emphasis may be lost.