We welcomed home a rescue ourselves back in August, and found he also suffered from some separation anxiety when we were out (specifically barking and howling). My first recommendation would be that she should get a crate for him, if she doesn't already have one. Something we found really useful as well was to get our boy to spend time in his crate alone (we leave a cover over it) while we are in the house. That way he could get used to not being right next to us all the time.
Desensitisation exercises are also really useful (if you search for it you'll find loads of previous threads on the subject). Basically, what it does is get the dog to stop associating your leaving routine (putting coat on, getting keys etc.) with you actually leaving. So this involves repeatedly putting on your coat, gathering your things etc. but not leaving the house. Sometimes we'll do this and then sit in them while we have a cup of tea before taking them off, other times we'll put them on and then immediately take them off, etc. Other exercises include varying the length of time you leave the house. So for example to start off, she might go through her leaving routine then go outside the house, lock the doors etc. only to come straight back in. With a dog that has separation anxiety it might take quite a while to build up to being able to leave the house for any amount of time.
Our boy went from spending all his time outside in a kennel to being inside with two humans at all times. Although he loved every second of it straight away, it was very confusing for him. I can only imagine that everytime we left he would be afraid that we would never come back and therefore howl/bark in order to get us to come back. It's taken a lot of time and patience, lwe've had him for 6 months now and only just are we able to leave him for 2 hours at a time without any problems. However, it's differnt for every dog, and the amount of time it takes to help them overcome their separation anxiety is different for each dog.
You might recommend the COL forum to your friend, as I said there is a wealth of information on here regarding separation anxiety and all the other antics that cockers can get up to. Also it's a great source of encouragement and advice for those really frustrating times when it feels like you've done everything you can and nothing has worked. I wish your neice the best of luck with her new cocker. I can't tell you how rewarding it is to take on a rescue and see how much they flourish in so little time!
