So to sum up, it wasn't HER, it was the wine. I've heard that excuse before.
Therefore this can actually mean "These are her wines", although I don't know if the course creators would be willing to include such translation ;)
That is allowed because in "To jest/To są" constructions, jest and są are not needed, and therefore it allows for this interpretation, even though it's "To (jest) jej wina" for fault and "To (są) jej wina" for wines.
Google translate says - this is her wine = to jest jej wina and this is her fault = to jest jej wina. So i guess context only gives the meaning or am i missing something vital here?
Google Translate is not a reliable source ;)
"This is her wine" (singular) = To (jest) jej wino.
"These are her wines" (plural, bottles of wine) = To (są) jej wina.
And "This is her fault" = To (jest) jej wina.
So on the level of omitting the form of "być", which is possible here, sentences 2 and 3 may be identical.