dainty

English as a Second Language English Vocabulary, Grammar and Idioms
1
  1. Since she ate always daintily, she looks always slim and dainty.
  2. She sipped daintily from her teacup and took half an hour to finish it.
  3. The food was tasty but was served in dainty proportions.
    Please correct all.
    Thanks.
2

I don’t think your use of ‘daintily’ is correct. Consult a good dictionary. Note that the adverb ‘always’ comes usually before a DO/HAVE-verb (single component) and after a BE-verb. When a verbal has two or more components, it comes between the first two.

(He always eats dainty food. I always have a book with me while travelling. They are always late to the meeting. You have always been posting good questions, I would say.)

3

2 and 3 are fine.

It’s only 1 that is problematic.
The sentence should grammatically read:
Since she always eats daintily, she always looks slim and dainty.
but logically, that does not follow, because ‘eating daintily’ means eating in small bites and not necessarily eating small portions.
Logically, it would need to be:
Since she only eats small portions, she has always been/stayed slim and dainty.