This sentence is wrong because it contains a double negative:
"She hasn't never been to London."
Can I use the word "ever" in this kind of sentence? Yes!
She hasn't ever been to London.
Don't ever lie to me!
Not ever = never
But not ever is much less common, and you cannot move it to the front as you can with never.
Never have I ...
How precise do you need to be? I'd just say
The circle is in the top-left corner of the rectangle.
If I needed to be precise then I'd set up a system of coordinates.
The expression "off to" is used in the phrase "off to one side". This has a negative meaning of "not central".
The garden has a lawn in the middle and a tree off ...
Your proposed correction to the sentence
She hasn't never been to London.
is correct. Just leave out the not.
As for your other doubts it is perfectly in order to use ever in an affirmative
I have never done X
I haven't ever done X
The parallel questions also work
Have you never done X?
Haven't you ever done X?
These are equivalent too.
 Sort [by extension].
 We came [by the back road].
In these examples "by" is a preposition functioning as head of the bracketed PPs (preposition phrases).
In  the PP is an adjunct expressing how something is to be sorted.
In  the PP is a complement of "came". PPs expressing path are complements because they
have to be ...
The first option sounds better to my ears, but either option is grammatically correct. But I would go so far as to say the second option is somewhat awkward. I think when you have an adverb that is five syllables long, you usually put it after the verb. And by putting the adverb after the verb, you're putting slightly more emphasis on the adverb by virtue of ...
You are quite right. The sentence "She hasn't never been to London" is incorrect because of the juxtaposition of two negatives "not" (contracted) and "never". You can correct this in any of your three suggested ways: remove the first negative ("she has never"), remove the second ("she hasn't") or make the ...
No, “right upstairs” does not mean they definitely live on the closest floor above you. In these contexts, “right” means somewhere between “very close” and “not far away”. It is used when someone wants to emphasize that a location, thing, or person is nearby.
Maybe it is surprising that a location is close:
Wow, I can’t believe I met someone in London that ...
Dictionaries show that 'only' can mean either:
limited to not more than, OR is not anything other than, the people, things, amount, or activity stated
Only (Cambridge Dictionary)
Translators of technical documents, instructions, etc, should make sure they understand the exact intent of the original-language writer. If the instructions are intended to state ...
Turn on the white light assumes that there are lights of different colours and you want the person to choose the white light.
Turn on the light whitely - I have never heard anyone say this, nor do I expect to. It sounds wrong in English.
I do not know what it would mean to do something whitely. Maybe you are dressed as a ghost in a white sheet when you turn ...
“Keen” is not a synonym of “interested.”
In your example, it has the sense (quoting from MW) of “intense.”
It is distinguishing between “mildly,” “moderately,” and “greatly” interested. “Keenly” clarifies the degree of interest.
For the first sentence:
Does more modify the verb care or the preposition about?
More modifies the verb care.
For the second sentence:
What word does more modify?
It also modifies the verb care.
The preposition about:
Can I use more to modify about?
Last question: is there any general rule?
Yes. In this case, you want to put this adverb as close to ...
way out is usually used to mark the route to the exit. way is an abstract concept, not a real thing. It could be a doorway, a corridor, a path, a stair, or any combination other these things.
road and door are real things: you can see that a door is a door, a road is a road etc, so the is no need to include the word door on a sign that is attached to a door.