In the book, Anne is very pretty and elegant, the words "very pretty", "lovely", "beauty", "elegant" are used to describe her in several places. In chap 1 --
"A few years before, Anne Elliot had been a very pretty girl, but her bloom had vanished early; and as even in its height, her father had found little to admire in her (so totally different were her delicate features and mild dark eyes from his own)".
So Anne is very pretty, but her features did not resemble her father's, it was Elizabeth's features which resembled her father's so Sir Walter regarded Elizabeth as very handsome. It is Mary who is the least pretty of the sisters -- chap 5 --
"In person, she [Mary] was inferior to both sisters, and had, even in her bloom, only reached the dignity of being "a fine girl."".
At Lyme, Mr Elliot instantly admired Anne, when he saw her on the beach with Louisa and Henrietta -- chap 12 --
"Anne's face caught his eye, and he looked at her with a degree of earnest admiration which she could not be insensible of. She was looking remarkably well; her very regular, very pretty features, having the bloom and freshness of youth restored by the fine wind which had been blowing on her complexion, and by the animations of eye which it had also produced. It was evident that the gentleman (completely a gentleman in manner) admired her exceedingly", and when they bumped into each other at the inn -- "this second meeting, short as it was, also proved again, by the gentleman's looks, that he thought hers very lovely,".
And at her reunion with her school friend Mrs Smith, it says chap 17 --
"Twelve years had changed Anne from the blooming, silent, unformed girl of fifteen, to the elegant little woman of seven-and-twenty, with every beauty excepting bloom,"
To portray the very pretty, elegant Anne as plain and dowdy is absurd.