First, from the photos we took of your Poinsettia leaf, we think your plant has something called Botrytis gray mold.
Here are a couple web links that detail how we came up with the pathogen we feel your plant is suffering from:
With this link, look down at the Foliar Problems section.
As mentioned in our phone call, one of the causes of this problem is watering the leaves of the plant. Moving forward we’re suggesting you water only the soil around the plant, with watering in the morning to allow the leaves to dry if they do get wet.
Other things to do to help eliminating this problem:
• Scout regularly for rust diseases.
• Frequently remove all rust-infected leaves. After removing, dispose of in trash, away from your garden area.
Use of a fungicide is recommended to assist in eliminating the problems your Poinsettia is having. Here is an organic fungicide that available at Lowe’s in Kahului:
Please follow the instructions on the fungicide as it’s easy to ‘burn’ your plant when applying.