What is the best way to correct this sentence? When Sheila and Laura got home, her dog was waiting by their front
door, its tail wagging as hard as it could.

When Sheila and Laura got home, her dog was waiting by their front door it was wagging its tail as hard as it could.

Explanation:

Hope this helps.

his tongue, i believe, was bloody and hanging out of his mouth.

he looked as if he were hungry.

he has several wolf-like qualities; a gray coat, sharp claws and yellow fangs.

those eyes made me feel, dear reader, like the end was near.

as i reached for a stick, he moved to the other side of the hill.

panting and hungry, he looked at me, a defenseless human and he snarled.

well i said my prayers, however, he simply turned and limped off. 

the best sentence that shows the best placement for the modifier "on the ice" is the one which contains it in the end of the sentence or in its beggining followed by a comma, that indicates it works as adverbial, dislocated in the sentence.

the girl promptly slid on her rollers on the ice.

on the ice, the girl promptly slid on her rollers.