Emmie, did you get her from a rescue organisation? I am very surprised that they have let an unvaccinated, unchipped, unspayed bitch needing dental treatment out to a home. 
When a rescue dog is new, it's natural for them to be following you around for the first few days. Everything is very new and they are still finding their feet. As she gradually becomes more settled, she will be more comfortable about being left to her own devices. The panting would have been a sign of stress too - if she's stopped, that's a good sign.
With the loss of appetite, there could be several reasons. Again, the stress of a new home. How is the weather with you? All of our dogs noticeably lose their appetite when the weather is very hot. It might be that she is unused to the food you are providing, or even that she has a mouth problem that doesn't let her chew hard food, especially as she has bad breath.
Another possibility since she is unspayed is that she is coming into season. This can affect bitches behaviour, appetite, drinking etc.
You might find that giving her something to chew will be helpful. As well as being very good for her teeth, chewing helps dogs deal with stress (act of chewing releases a feel good hormone). Try something like Stag Bars, pigs ears occasionally, a Kong stuffed with treats, or a large raw bone from your butchers.
The rescue where you got her should be offering you backup and support, but as they have let her be homed in this state, I am not confident.
Good luck! It sounds as though as she has had a rough start in life but will have a very loving home with you, and it's lovely that your parents also have a Newfie to keep her company. 