1.The dog followed Mary
2.It followed her for half a mile
3.It stayed very close behind her
4.She forced herself to stay calm

Mary forced herself to stay calm while the dog followed very close to her for a half a mile.

The dog followed Mary for half a mile, and stayed very close while she forced her self to stay calm.

The dog stayed very close behind Mary while following her for half a mile, so she forced her self to stay calm.