The timing is wrong at this stage
Written by Tracy W
(6/4/2007 6:01 p.m.)
in consequence of the missive, Slow-moving aunts, penned by Sansanee
The next chapter specifically states that only then did Mr and Mrs Gardiner realise there may be an attachment.
Her uncle and aunt were all amazement; and the embarrassment of her manner as she spoke, joined to the circumstance itself, and many of the circumstances of the preceding day, opened to them a new idea on the business. Nothing had ever suggested it before, but they now felt that there was no other way of accounting for such attentions from such a quarter than by supposing a partiality for their niece. (chpt 44).
Since this idea only occurs to them after the initial visit to Pemberley, I don't think Mrs Gardiner was plotting anything there.