What training has Maggie had?
Did she always sleep in your wife's spot on the bed?
I think the problem is Maggie is under the impression she runs the house now. All that kindness she sees as you putting her in the leader role which is why she is 'bossing' you when she thinks you are not obeying her.
Letting her sleep in your wife's spot on the bed is one of the ways you accidentally put her status up in her mind. She believes she is 'owner' of the bed, her crate, the food, you etc. As such in her mind she has the right to correct you to make you mind your manners.
There are some things you can do that will help you with this mistake she has made.
I'd suggest joining an obedience class with her and http://www.apdt.com/ may help you find one to participate in. I'd suggest clicker training and this site has some videos down past the ads to show you what that is about
http://www.clickertrainusa.com/clicker-training-videos.htm
I'd also suggest some new house rules for you including using the nothing in life is free program to change her mind about who the leader is at your house. You can read about this non violent method of putting yourself in the leader role here
http://www.paws.org/cas/resources/fact_sheets_dogs/nothingfree.php
Most often I would say 'no dogs in the bed' but I do understand why having her there is a plus for you so instead of that I'd suggest removing the pillow on that side of the bed, not letting her on the bed until invited. And practice with reward training her getting off the bed on command.
Hope this helps you!
Nothing you say sounds like its anything really beyond the dog has taken over and is in charge and is punishing you for being 'bad' in her mind and by her rules.
Serious biting removes muscle tissue, takes chunks out of a person, requires medical care to treat etc. I don't get the impression you are describing that.
I do think she is terrorizing you because she thinks she is the leader.
Now this might be due to a medical issue such as a low thyroid, a tick carried disease or possibly a seizure problem. But that would take vet care to resolve.
I suggest you try the nothing in life is free program with her and follow it for a week or ten days and see if you see a change in her behavior with you. If the answer is yes then the problem is her thought that she is the leader not you. This is moderately common in dominant or pushy dogs when they hit 3 years old which is when dogs become fully mature pack members.
On top of everything else the female 'pack leader' is gone from her life so that leaves the position open, in dog terms, for her.
The problem with dogs is if they do not have a strong leader (I mean strong as in personality and leadership not physical strength) they presume they must be the one running things.
If you are frightened of her you might see if the breeder will take her back even if its just for a short break for you two to be apart so you can start the relationship over.
I've retrained a lot of dogs with similar issues. One dog had 9 homes because he learned if he bit people he could get his own way. That didn't work here and he became a great pet and went on to a good home with a strong leader in it where he became and agility champion.
If this is not a medical problem then its likely a training issue and you can choose to try changing how you behave with her using NILIF to see if that works.
Dog Expert:Rescue, Train,Breed,Care
30+ yrs dog home vet care & nursing, rescue, behavior&training, responsible show breeding, genetics
The chest lump is probably a fatty cyst. The thyroid is up under the throat area.
All of what you say really makes me suspect that this is an accidental case of Maggie thinking she has been elected queen of the universe due to your kind attentions and catering to her wishes.
But as I cannot see the dog in person I cannot be 100% sure of that.
Tick carried diseases and thyroid problems and other health issues can cause behavior changes and your vet would have to check for that sort of thing.
An in person evaluation by a trainer may help but perhaps the rescuer knows someone who can do that for you for free.
Also beagles can have seizure episodes and depending on where in the brain a seizure happens that can cause aggression to show up suddenly.
But really all those descriptions to me fit under the 'boss dog punishing lesser pack member for rule breaking' including the direct look in the eyes etc.
No problem I was glad to help you and I really do suggest trying NILIF with Maggie and see if you can 'unelect' her as ruler of the universe and see if that helps!
the site sends messages I don't control I appreciate the above accept!