Why are some people so confused about this film? *spoilers*
The entity's nature was to destroy the humans' spirit, to destroy their hope, and feed on their fear. To break them down.
Everything the entity did was to accomplish this, including showing her her boyfriend being consumed by the evil.
Another example, the dog died because it mattered in a way to the Ashley Greene character. She was a vet tech and loved animals, and the dog was visiting her.
That's why the cactus died too, because the female character liked it.
The entity did everything it could to destroy their spirits, break them apart & down.
At the end of the film, her mind was all but gone, her spirit completely broken. She went to Costco's tents because it was a good memory of when she went camping with her dad, felt safe. And she had a recent good memory of discussing camping with her now-lost boyfriend.
We see that she finally did give up, they broke her spirit at last. And it/they took her.
The film implies this is only the beginning. Now that they're here, they will continue to take more and more humans. The film needed a tighter script, and more action, but the premise of it was very good and very chilling.
The ending and its IMPLICATIONS (see ending of: 'In the Mouth of Madness') is hair-raising.
"I'd say this cloud is Cumulo Nimbus."
"Didn't he discover America?"
"Penfold, shush."