1. 'B'nai Elohim' does indeed mean "Sons of God" because it's referring to Yahweh who is single in Being but plural in person. "Elohim" was a title not a name like "god" and could be used to refer to multiple gods.
2. The fact that some of ancient Israel did worship other gods alongside or instead of YHWH does not mean that they were supposed to or that there was some progression from polytheism to monotheism. The Bible is really clear that there was polytheism even in Genesis forward, from many people, including Abram's extended family, but not Abram himself.
She correctly shows that many people disagree that with what the passage means. Her opinion is definitely from a non-believer. So how about after reading Cathy Cooper's take on the passage, whose conclusion I don't come agree with and is linked below:
Debunking Christianity: What Happened When Humpty Dumpty Met the Sons of Gods
Watch and listen to Dr Hank Hanegraaf answer the question and other relevant questions.