It sounds as though perhaps she needs a bit more mental stimulation. I have a 14 month old cocker bitch and she too gets lots of walks, but also needs lots of mental stimulation to stop her getting bored. Remember they are gundogs and therefore very intelligent - they need to have their minds excercised as much as their bodies.
A few things that might help would be:
1. If you don't have one, go to your local pet shop and buy a Kong - stuff it with things like mashed banana and yoghurt - initially with things that are easy for her to get out.
2. You could also invest in a treat ball - you put dry treats or kibble into it and they have to work out how to roll it around the floor to get the food to drop out - this keeps Bella busy for ages.
3. If she likes shredding, which Bella does as well, you could create something for her to shred that is safe. You could for example get a big cardboard box, cut some cocker sized holes in it, stuff it with newspaper etc and hide some treats in there. Whenever I leave Bella I always get something like an old teabag box and hide treats in newspaper inside and she shreds away to her heart's content - this way she can get that out of her system on safe things and doesn't tend to shred anything else in the house.
You could also try doing things like scent games with her, cockers generally love things like this, eg show her a tasty treat, put her in the next room and hide the treat, then let her in and encourage her to find it. You'd have to put it somewhere easy to start with but you can then make it harder for her and it will use up her gundog instincts finding it. You can do the same getting her to find toys.
Have you taken her to any obedience classes or anything - are you able to get to any? This might also help as it will be great mental stimulation for her and of course you'd be taught different methods to get her recall better.
If she is 12 months she is very much still a teenager so she will be a bit testy at times, it takes patience as you already know. I would practise her recall as much as you can and give her a good, tasty treat when she comes to you to encourage her.
I really hope you can sort out your problems with her so that she doesn't have to be rehomed.