You're not falling at the first hurdle Sheryl, you're (quite rightly) worried about your little girl.
I would imagine that Lyla is just very pleased to be home. She'll be exhausted from everything that has been going on, both physically and emotionally (being away from you).
She'll be very sore from being moved today. If she's coughing that will also be hurting her. I would leave her to rest in her crate, move her as little as possible, and leave some food (with the rimadyl in it) in her crate. My guess is that once she's had a good few hours sleep, she'll eat her food.
The growling is, as you said, because she's sore. If you have to move her then use a cloth muzzle, but remove it as soon as you can (I know you would anyway).
I'm sure you know how to test for hydration (pinch the skin and if it returns to shape she's fine, if its stays pinched, she's dehydrated). She's been on a drip at the vets and so will be have been hydrated when you bought her home, she should be fine without drinking for a good few hours.
Its really daunting isn't it, going from having your dog cared for by a team of experts to suddenly having to do it on your own, but you're the expert on Lyla, she's best off at home with you, try not to panic, just let her rest and let her heal