My kids are the same. I usually give them fill in the blank paragraphs like this:
My favorite animal is
a dog. I like
dogs because they are
loyal, funny, and cuddly. I have a pet
dog named Ralph. Ralph is funny because he likes to play fetch with himself. Our favorite thing to do together is
snuggle under a warm blanket. I love
They have to copy the underlined parts and fill in the rest as it makes sense to them. My kids have serious processing disorders. For some reason they cannot handle processing what you are asking them to write, plus their verbal response, plus getting that down on paper. It's like having something "on the tip of your tongue" that you just can't get out. My kids always have something on "the tip of their fingers."
If they do free write it comes out more like this:
My favorite animals is are a monkey and monkey running to the store and it funny.
....with more misspellings.
Sometimes I feel like they just string random words and verbs together. To keep me from jumping out the window and to help them feel success, the fill in the blank works best for now.