The words are not synonyms, however in common usage, people don't know the difference and so use them as they see fit, thinking they are synonymous.
Strictly speaking, a comment is a written note intended as an explanation or criticism of a passage in a book. It is a kind of annotation. The word comes from Latin where it means "interpretation."
To remark is to express briefly as a comment. Remarks are spoken:
"What do you think of my hair?"
"Looks great," he remarked.
"I hope he takes a long walk off a short pier," he remarked sarcastically.
Comments are longer, usually in print, and interpret and give extra information. They state an opinion and do so in a longer way than a remark. However, comments can be spoken:
"Mr. President, would you mind commenting on today's deal with the labor union?" In this case, the president would not say "It's great." I suppose he could, but at the level of president, a comment should be lengthy and should help people understand something. If the president were to respond "It's great" my guess would be people present would laugh, as they would be expecting something of more substance than a throw away remark. So in the above example, the president might speak for a few minutes. Comments would not be statements about what the deal was, but would be his interpretation of what the deal means, implications for the job market, and why he supports or doesn't support it.
In your example, in my opinion, it would be better to use comment: She made a helpful comment on my work.
If you look online for definitions of these words, you will find many dictionaries that define the words rather loosely, so it is difficult to distinguish the meaning.