I need help identifying this plant, it may have made my dog sick.
After some super input from 'someone else', we should consider Arctium lappa or Common Burdock. These leaves in the picture are of a plant without fertilizer and only periodic watering. Burdock leaves can get huge with lots of water and a bit of fertilizer! Look at the margins, overall shape, color and if we were to pull that plant out of there we could see that root.
If this answer is correct, then I doubt this caused the puppies any sickness. I'd like to hear what the symptoms of those puppies were? What the veterinarians have found. Please say they are fine now, those puppies or puppy is still fine?!
This plant is definitely burdock. Its leaves can become massive and in its second year it will send up a large flower stalk with seeds that mature as spiny burs like velcro that will stick to your clothes. Cool plant - has medicinal qualities. Leaves are extremely bitter so I doubt your pet would want to eat it! If you want to remove it, dig out as much of the taproot which can get very deep as you can.
After a bit of research this looks like Digitalis or Foxglove.digitalis picture of leaves
How are your puppies/puppy/dog? What were the symptoms? After looking at the pictures I sent you, does this plant look familiar?
Foxglove is very poisonous. Let your veterinarian see these pictures, they SHOULD be well versed with poisonous plants for dogs and cats! So MANY are in our yards!! When your pets are outside they should be supervised and taught to not eat any plant material. Cats are far more vulnerable as people allow them to become the 'neighborhood' cat (grrrrrr) and ALL lilies of all kinds are very poisonous to cats in particular but dogs as well.
What other plants are in your yard?