Daisies are edible (and tasty!)
The best to eat are young flowers, just after developing. Old flowers are not poisonous, but not so tasty. Young flowers are soft, and delicate.
The taste is mild. Some people say, they sense the delicate flavour similar to radishes. Maybe a little bit, but daisies are not spicy. I find daisies taste more like a salad with flower aroma.
You can decorate sandwiches, add to the salad, decorate a cake. You can also add flowers to tea. You can use fresh flowers, or dry flowers in winter. Due to the delicate flavour and pale colour daisies should be the additive rather than the main ingredient. I drink them as an addition to the weak black tea. The aroma of flowers is clearly perceptible and enjoyable.
Remember to collect the daisies with a clean lawn, away from the highway pollution and away from herbicides, pesticides spraying in orchards or some gardens. Make sure that your neighbour does not spray plants. If you need to spray your tree in an orchard, remember that tiny droplets of the spray can float far. The grass near the tree can be sprayed as well. You should check protection period on product labelling, after that period your daisies will be good to eat. It should be in the instruction. Typically it is 2 or 3 weeks.
If you buy daisies for the garden it is better to wait 2-3 weeks before eating - they could be sprayed during growing.