Puppy

sorry, that should have been does your puppy ........

Does our puppy have a crate/indoor kennel to sleep in at night.

If not I suggest you get one. Encourage her to go in it when you're in the same room and to sleep in it at night. Our dogs have one each where they sleep and when we're out.

They feel safe and secure so much so that our cockapoo who had very bad separation anxiety is absolutely fine now when she's left.

Sorry, mine is not a dachshund.

I think it is very much a puppy thing. Ours is a bit younger than yours and whines for a while when we leave him, but on our return he is as quiet as a mouse and has definitely been asleep. Luckily we don't have joined on neighbours. He has loads of toys to play with and we leave the radio on when we go out. Our longest stretch was 2 hours so far. He is our 5th puppy, some more needy and vocal than others, but it does subside eventually. Good luck.

Have you had a chat with your neighbours and apologised? That would diffuse any irritation they might be feeling especially if they then know you’re doing your best to resolve it. Is the breeder of any help? The woman I got my latest dog from offers lifelong support. She’s just bred a litter of Black and Tan dachshunds and I must say they’re beyond gorgeous! Are you on a dachshund Facebook page? Such groups are great for advising on problems common to their particular breed. I agree about puppy/training classes. A good trainer won’t just train but will offer advise on other things. From the dachshunds I’ve known some seem to be far more yappy than others. I do sympathise. I had a barky spaniel for 14 years and she drove me nuts.

When you say that you've tried all the normal cures, I wonder which? In my experience, it's a long job of consistent training basically teaching the puppy to be alone in the same secure place in the house while you're in it too and then very short periods while you're out. I've found a good guide, link below, which you may have already found.
Our next door neighbours currently have a puppy which shrieks incessantly the moment it's left which isn't great for neighbour relationships.
You might need to get help if you can't cope yourself. Puppy classes for general training are a good idea.
"Separation Anxiety in Dogs Alone at Home | Blue Cross" www.bluecross.org.uk/pet-advice/home-alone-separation-anxiety-dogs

I don’t own a dog, but my son and daughter in law now have a pup and decided to go to puppy training classes. What a difference it has made to the behaviour of their puppy. In a matter of weeks she has become an obedient and lovely pup to be around.
I hope you have some classes nearby that you might think about.