One common assumption people have who are not chemically sensitive is that all scents are bad. If perfume causes reactions, it stands to reason that flowers that have a strong scent also cause reactions. This is not the case. Flowers are fine, pesticides and herbicides are not. As with every other grown item the floral industry uses pesticides and herbicides to protect their product during growth, cultivation, and transport.
Therefore avoid floral arrangements unless they’re organic (flowers are organic material and in of themselves but what I’ referring to here are flowers grown without the use of pesticides or herbicides). If you would like to send someone flowers who is chemically sensitive, make sure they’re pesticide/herbicide free, and that you tell the recipient that they’re “safe” flowers. Otherwise grow your own flowers and use those cuttings. Flowers under those conditions are fine.