what purpose does the accent serve? based on how she pronounces it, that syllable doesn't carry the stress.
In portuguese language, ALL the words carry the stress on one of the last three syllables. If it's on the last syllable, the word is called "oxítona". If it's on the second from last, the word is called "paroxítona". And if it's on the third from last, the word is called "proparoxítona". ALL the "proparoxítonas" have accent. Pe-rí-o-do fits that rule.
OK. Thank you. That's what I thought, and it's why I was confused. She seems to pronounce it like a "paroxítona" word instead of "proparoxítona." So it should be pronounced "pe-RI-o-do" and not "pe-ri-O-do" as she pronounces it?
This is one of those "exception" words. Anyway, the second to last "o" is pronounced as "u", as you can hear. "pê-ri-u-dô". If it were a "paroxítona" word you would pronounce it as an "ô": "pê-ri-ô-dô". That's why it is a "proparoxítona", I think.