The line from "Helen Grey" that implies the author thinks physical beauty is not the most valuable quality is But so you miss that modest charm / Which is the surest charm of all
Explanation:
The line uses the words "the surest charm of all" which means that it doesn't have much to make it special, in the lines before and after this one we have more key information that implies the same as it says that Helen Grey should be so proud of being beautiful since that is a quality that would make her important in life.
