The wedding speech for sister of the bride should mention how beautiful and stunning the bride looks. Personally I think it is a great way to start the speech off after you introduce yourself.
As sister of the bride one of your unspoken responsibilities to the bride on her wedding day is to tell her how beautiful she looks. It doesn’t matter if she has a zit in the middle of her forehead or got over-sprayed at the tanning booth – you reassure her that it looks fine and that she looks more beautiful then ever. You just need to make her feel like a beautiful princess – if she’s worried about how she looks then she can not relax and enjoy the day. (Just remember you can always ‘airbursh’ the pictures afterwards!) A lot of guests will tell her how beautiful she looks but it is your responsibility to include her beauty in your wedding speech for sister and make a public acknowledgement.