2 Added explicit answer to specific question.
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You are right.
When 'however' is used correctly, in most cases, you could simply remove it from the sentence and it would still be correct:

Characters in the novels are not always morally and socially obliging to each other, but there is differentiation between the upstanding hero or heroine and the socially less acceptable characters.

He asked me for money to buy a sandwich. I did not have enough money for a sandwich, however, but I gave him what money I had.

Perfectly fine. Her correction is wrong.

You are right.
When 'however' is used correctly, in most cases, you could simply remove it from the sentence and it would still be correct:

Characters in the novels are not always morally and socially obliging to each other, but there is differentiation between the upstanding hero or heroine and the socially less acceptable characters.

He asked me for money to buy a sandwich. I did not have enough money for a sandwich, however, but I gave him what money I had.

Perfectly fine.

You are right.
When 'however' is used correctly, in most cases, you could simply remove it from the sentence and it would still be correct:

Characters in the novels are not always morally and socially obliging to each other, but there is differentiation between the upstanding hero or heroine and the socially less acceptable characters.

He asked me for money to buy a sandwich. I did not have enough money for a sandwich, however, but I gave him what money I had.

Perfectly fine. Her correction is wrong.

1
source | link

You are right.
When 'however' is used correctly, in most cases, you could simply remove it from the sentence and it would still be correct:

Characters in the novels are not always morally and socially obliging to each other, but there is differentiation between the upstanding hero or heroine and the socially less acceptable characters.

He asked me for money to buy a sandwich. I did not have enough money for a sandwich, however, but I gave him what money I had.

Perfectly fine.