I think she was being nice and appreciated your comment.
A word used to describe what girls think are anything cute, sweet, sad, good or bad. aww definition by Urban Dictionary.
It's English for, "Ah, so..." One of those things we say when we don't have the words to say them.
Aww (spelled with 2 or more "w's" is frequently followed by "How cute" or "That was so nice"; but the two phrases are not always spoken.
It's a sign of positive appreciation for what the person saying it thought of your comment.