My wife is telling me that she bought it as aromatic garden plant It is now 3-4ft tall and blocking the view of a rose behind it
This looks VERY much like wild parsnip, which is a plant you need to remove as soon as you can.Here are some images to help with the ID:
If this is wild parsnip, it's an invasive and potentially dangerous plant, so BE CAREFUL when removing it! The sap is phytotoxic and will cause chemical burns if it gets on your skin in the sunlight. The sap can also cause damage to your eyes. To remove the plant, wear long sleeves and gloves (and eye protection, if possible), cut the plant down to the ground (and dispose of it in a garbage bag), then dig out the root. This is nasty stuff that you do NOT want to set seed.
EDIT - It's possible that the person/store where you wife bought the plant thought that it was Golden Alexanders - it's certainly NOT that plant.