She frequently attacks our older dog (he's 1 1/2) and this morning she snapped at my face. She snarls if we try to shift her position on the sofa, and when I tried to clip her nails she struggles and snarls.
What are the circumstances leading up to the attacks and the snapping?
You shouldn't be trying to shift her - would you be happy if you were lying on the sofa and someone 20x your size came along and forced you to move? If you want her to move, you need to ask her - lure her with a treat or use a house line if necessary. The expression "let sleeping dogs lie" exists for a reason, lol.
She seems to hate other dogs, she's fine until the dog comes near her. She's obviously wary, but not necessarily afraid. She's fine with people and us most of the time, happy, and will actively seek out, follow, and sleep with our older dog.
What makes you think she hates other dogs?
She has major food aggression too.
Do you leave her alone when she has food and treats? You shouldn't be interfering while she's eating or has a treat. Just feed her in a safe space (behind a baby gate, in a pen or in a crate) and leave her alone. Don't give her a reason to get defensive.
Have we got a duff dog? Can we do anything? She's here to stay unless she becomes super aggressive, obviously. What are the causes of aggression? We love her, and really want to sort this.
To be, it doesn't sound like she's aggressive - it sounds like she's expressing herself in the only way she knows how. Have you read up on the ladder of aggression, for example? Do you notice and pay attention to her warning signals - lip licking, showing the whites of her eyes, putting her ears back, grumbling/growling?