I agree it is unusual for a beagle to be aggressive - but I wouldn`t say they were naturally submissive dogs either. I have a beagle cross who was extremely bossy when I got him - stealing food, fighting other dogs, shoving people out of the way etc. He was demoted fairly rapidly and muzzled for a while till he learned manners. He is now a model citizen (most of the time).
This isn`t a failure - it`s a problem to be dealt with. Up till now you`ve been lucky, so be thankful for that and get on with a bit of remedial training. I`m sure it`ll soon get sorted with the help of a good behaviourist. In the meantime, why not use a house-line on the dog, and maybe stairgates to restrict her access might be a good idea until you get a new regime sorted. Good luck.

Not heard of an aggressive Beagle before but anything is possible, especially if it's got teeth. I agree with the others about taking her to the vet to get her checked out. Has she had a season recently at all, it might be a hormonal thing. I would also take her back to basics and instill in her where the boundaries are. Since her aggression seems to be during her moments on the sofa I would remove the sofa from the equation. Make the no going on the bed rule a no going on any furniture rule until you learn some manners rule. Another benefit to her not being on sofa means it removes her mouth from your husbands head height.

Out of curiosity, when do you feed her, is it before or after you eat? We've always fed our dogs after us so they learn they place in the pack so to speak. In a natural situation it's always the dominant pack members who eat first and the lower ranking dogs who get the left overs.

Heidi

hope all goes well at the vets but does sound to me that she is domenate as you said that she is boss over the other dog.
you need to think about how you act with her, does she jump up on the sofa or will she sit and wait untill you or hubby invite her. its the little things like that that tell a dog that they are in control and not you, also if she comes up to you do you give her the attention she is after or do you make her sit first or wait untill you are ready.
you need to be instigating things and not the dog, as if she is you are following and she is leading and it should be the other way round. hope this helps and gives you some ideas to be going on with

I can imagine how worried you are, good luck tomorrow at the vets and hopefully they can recommend a good behaviourist to help sort it out.