"I am finished with the website for now".
First of all, there's nothing inherently bad or wrong with using passive voice--often times, it is the better way to construct a clause.
Now, with that aside.
Does your example use passive voice? . . . Superficially, it might appear so, to an automated grammar checker.
A traditional grammar's version of a passive (voice) sentence is a sentence that involves a construction whose lexical verb is a past-participle verb form and whose auxiliary verb is a form of the verb "BE" (or of the verb "GET", in some uses).
Your example has the expression "am finished". The word "am" is a form of the verb "BE"; and the word "finished" has the shape of a past-participle verb form. But that is the crux of the matter: Is the word "finished" in your example a past-participle verb or a past-participle adjective?
There are some grammatical diagnostic tools/tests that you can try out to come to your own decision on this. One diagnostic test that can often be useful is the below--Is the candidate version similar in meaning to an active voice version:
"I am finished with the website for now". -- [original version]
"Something finishes me, for now". -- [active version?]
Hmm, that doesn't seem to support the passive argument. Compare to: "Today, the neighbors finished the job"; "Today, the job was finished (by the neighbors)".
(Aside: There's also the prepositional passive: "George Washington slept in that bed"; "That bed was slept in by George Washington". But that doesn't seem to be relevant here.)
Another diagnostic test, which can sometimes be useful, to see if the candidate word is an adjective, is to try to see if the candidate word can be modified by "too" or "very":
- "I am very finished with the website for now".
Nah, that isn't convincing either. Compare to: "Tom is very tired".
There are other diagnostic tests that you can try (which might be in your favorite grammar books), but at the end of the day, you'll have to make the decision for yourself. (I have my own opinion.) Someone else may very well produce a convincing argument for you for one position or the other. Of course, your decision might also be influenced as to the grammar that you are comfortable with, and with how that grammar defines passive voice.
Passive does not invert its auxiliary be; it just inserts it and turns the verb to past participle.
Promoting the direct object to subject is not inversion, which is simple re-ordering of words.
The "must be turned into" part of your proposed transformation is wrong, with preposed only.
Inversion is not required with preposed adverbs, although it is optionally grammatical
with preposed negative adverbs of place, time, or circumstance (i.e, ones that negate the clause).
- At no time was the temperature changed.
- Nowhere may the temperature be changed from the thermostat settings.
- Under no circumstances is the temperature to be changed.
Only, however, is not one of those. If you try this with different adverbs, you get ungrammaticality:
- *With no instrument was the salami sliced by George.
- *In no particular way did she say the sentence.
- *Only is the temperature changed in the daytime.
Best Answer
John Lawler's comment sums it up:
Here's a paper that describes some relevant phenomena: "On the Grammatical Status of PP-Pied-Piping in English: Results from Sentence-Rating Experiments," by Seth Cable and Jesse A. Harris.
In English, the "neutral" position for question words is generally at the start of the sentence. Many grammatical analyses treat this as the result of a process, "wh-movement," that moves these words from another position.
Cable and Harris give the following example:
It's also grammatical to leave a question word in place ("wh-in-situ"), as in "She left who?", but in standard English this kind of structure is not the default: it's generally less appropriate than wh-movement except in certain circumstances (e.g. echoing a declarative sentence to express surprise). This is a valid stylistic reason why someone might object to your daughter's sentence. The teacher was wrong to call it "ungrammatical."
Sometimes, other words can also "move" with the question word. The term used for this is "pied-piping," since the idea is that the question word metaphorically abducts other words a bit like the Pied Piper of Hamelin abducted children.
This phenomenon is quite interesting to linguists so there has been a lot of study of it. When the question word is the object of a prepositional phrase (PP), it's generally optional to move the preposition to the front of the sentence along with the question word. Cable and Harris's explanation:
So the teacher's sentence "Whom was the vase broken by?" is not ungrammatical either.
However, it may sound funny because in general, the contexts where people use "whom" are also contexts where most people try to avoid preposition-stranding. (This point is also made by the answer to the following question: "Prepositions at the end of sentence and whom".) This would be a valid stylistic reason to object to the teacher's sentence.
As other people have mentioned, this consideration means that the following sentence might be the best, stylistically speaking:
However, a valid stylistic objection to this sentence is that to most people it sounds highly formal, old-fashioned, or pretentious. Most people would say, and many people would write
People could object that this sounds too informal. I think that's silly though, so I won't call that a valid stylistic objection. Using "who" in this position (not "whom") and stranding prepositions are both generally considered acceptable by educated people. But if the teacher is a pedant or "stickler," that might not matter.