And do you propose to stay or are you waiting for the trellis to dry?
Do you have to paint it then?
That rather depends if LL has chosen wooden or plastic trellis. If it is wooden it will need to be treated with a wood preservative every couple of years and certainly when first erected. If plastic it will crack in the sun, turn a paler colour than the one she thought she had bought (unless white in which case it will go yellow) and it will be all YOUR FAULT!