Add lilac flowers and coconut milk to a bowl or large jar and stir to combine. Cover with plastic wrap and refrigerate for 24 hours to let the lilacs infuse into the coconut milk.
The next day, bloom the gelatin by sprinkling it over water in a small bowl or ramekin and set it aside.
Heat the wild blueberries, sugar and salt together in a small saucepan over medium heat until the sugar is completely dissolved after about 3-5 minutes. Strain the blueberry mixture through a fine mesh strainer into a small bowl pressing the blueberries with the back of a spoon to release all their liquid. Set the blueberry syrup aside.
Pour the lilac coconut milk mixture into a medium saucepan and bring it to scalding temperature or just before boiling point over medium heat. Do not let it boil. Strain the mixture through a fine mesh strainer into a liquid measuring cup or pitcher, pressing the lilacs with the back of a spoon to release all of the milk.
Add the bloomed gelatin and still-warm blueberry syrup to the hot coconut milk and whisk until the gelatin is fully dissolved, about 1 minute.
Pour the panna cotta mixture into 4 glasses or oiled ramekins or molds if you plan to serve them unmolded. Arrange the glasses on a quarter sheet pan first so they will be easy to trnafer to the fridge.
Cover the glasses with an inverted quarter sheet pan or with plastic wrap and refrigerate them for at least 2 hours until the panna cotta has firmed up and set.
Garnish the tops of the panna cotta with lilac flowers. To unmold them from ramekins run a thin knife along the edges and place the plate over the top of the ramekin then flip it over and shake gently but firmly to release the panna cotta from the molds.