I was planning to make a huge post about the "we live inside a dream" line and the ending recently, but I gave that up, as there are aspects of the ending I just don't get at all.

But anyway, my general interpretation of the ending is that Laura is, indeed, living inside a dream/nightmare, and she won't get out of it until she finally faces a final, terrible truth about her past trauma : her mother was also a monster, as she was silently complicit of Laura's abuse. So really, the final episode is a battle that takes place inside Laura's soul : either she faces her demons and remember who she is and what her parents were, or she will keep living a nightmarish life of pure negativity.

I see several clues in the final episode indicating that Laura is trying to escape or ignore the truth about herself, her past and her mother ; and that this life of denial is a life that will never be freed of Judy's shadow, a demon or force of pure negativity that feeds on Laura's suffering and inhabits her mother, the silent witness of Laura's abuse by Bob. Laura lives a depressing life in a depressing town and works at a depressing restaurant called "Judy", where violent customers abuse the waitresses. Her house is right under a very significant electrical pole, and inside of it is a dead man that was probably a host of Bob that she had to kill. Inside the living room of her house, a pale horse can also be seen, a symbol that seems to represent the deaths and abuse that Sarah Palmer saw without intervening ("The horse is the white of the eyes, and dark within") because she willingly took the drugged drinks that Leland gave her, a ritual she continued afterwards by drowning herself in vodka while watching violent videos ("This is the water and this is the well. Drink full, and descend"). So Judy/Sarah's eye is still watching and feeding on Laura's suffering, even though she won't acknowledge it. Questioned by Cooper, "Carrie Page" doesn't react when she hears the names Laura and Leland, but she has a huge reaction when he tells her that her mother is Sarah Palmer. Even though Laura tried to escape her past, she did know the truth about her father (he was Bob all along), so he's not as a big a problem as he was before. But the monstrosity and responsibility of her mother is still an unresolved issue, and something that Laura never faced or acknowledged.

So the final episode is a journey, an "odyssey" Laura Palmer has to take inward to finally face the truth about her past. It's terrible, sad and painful, but it's the only way Laura will ever be freed of her past trauma and Judy's influence over her. Judy might be a negative force of nature or a demon, the source of the torment and suffering she creates and feeds on is still inside, in the soul, so that's where you need to go to find and fight her. As Lynch said in an interview about TM, the source of our problems is never outside : “The torment is inside the people, and you can’t change that unless you get down on a deeper level. So we are all like detectives trying to find that truth.”

So yes, it's "very important" that her guardian angel brings her back home to see her mother : she's everything that Laura won't dare to face. And what we see in the final episode is that slowly but surely, Laura starts to remember who she is, until she finally hears her mother's voice and understand everything. Facing the horrible truth, she screams her heart out and lights go out : this nightmarish dream/reality Laura was living in is over with, and a new one can begin. She finally faced and acknowledged the truth. Is it a good or a bad ending? A bit of both, really, but it's definitely an ending : Laura has finally come to terms with the truth and can begin to heal, but that truth is still a horrible tale of two parents abusing their child, be it directly or indirectly.