You are not raising a spoiled brat

These are my theories on what could be going on:
You are possibly raising a dog with a common behaviour issue in spaniels: Resource guarding. And if that is the case then it is not due to training, but just a problem some of them get. And the good news is that if managed correctly is possible to get control of.
The solution is surprising. Because we tend to think in terms of not letting them get away with bad behaviour. But when you understand where resource guarding comes from in the dogs mind then it all becomes more logical to take a step back and retrain them rather then physically forcing them. Because using force (however gentle and fair in our mind) will escalate the problem. I am no expert but I know many in here have dealt with it so there are plenty of advice to be had. I can also recommend the book "Mine! A guide to resource guarding" for all dog owners to read.
If it only happens on the sofa then you could just block access to it. Or better yet train Inca to jump up and down on command by using plenty of positive reinforcements. Training her to wait before jumping on the sofa could also help. If you do have to remove her physically then it is better to have a leash on her so you can safely move her not risking her snapping at you.
In addition to this I would train handling, just in case this is not resource guarding but an issue with being handled. Use positive reinforcement to make sure she is comfortable being handled and touched and pushed and pulled in different situations. If you are at all insecure and feel afraid then a behaviourist could help. Never take risks. But we can all benefit from training our dogs to be comfortable with lifting, gentle pushing and adjusting their posture. Your vet will also thank you in the future for a dog that is happy to be handled.
Another possible reason for her reaction is that some dogs just want to be left alone when they are resting and will communicate this by growling or snapping. If this is the issue, then teaching her to go to her crate or bed when she wants to be left alone could be the answer. Some are just grumpy when thay are sleepy and that's fine, but then they need to learn to withdraw to their "safe place" when wanting to be left alone.
All of the above are issues you can resolve by continuing to use reward based training. You have probably done everything right already just that she has some extra challenges you need to add to the normal dog training. I don't know if you feel I am correct with any of my theories, but don't be to discouraged there are trainers and behaviourists that can help you if it gets to challenging.