"after being baked in the oven for thirty minutes, her guests were given the cookies". does this sentence contain a "dangling participle"? can you explain why ?

Yes, because the clause, "After being baked in the oven for thirty minutes," doesn’t have an explicit subject, although from the context you’d expect it to be food. The next words you see (‘ her guests were’) are the subject of the sentence, but they clearly don’t match the preceding clause, because guests usually cannot eat cookies after being backed in the oven.