A sunny spot
She'll be happiest if she gets around 4-5 hours of sunlight a day, so make sure she's in a well-lit spot.
Diana needs well-drained, alkaline or neutral soil to thrive, try not to let her dry out too much.
If one of her flowers look sickly, give them a little snip with a pair of secateurs. Make sure you cut just above one of the leaf nodes to encourage new growth.