Wires can be soft, though it's not an acceptable show coat. Were both Stella's parents wire? Technically, breeders aren't allowed to cross breed coat types, though byb's often do. It's said that wires are hard to get a good uniform type of coat due to incomplete dominance of the wire gene with a recessive long or smooth gene.
Here's a quote from Dachshund colors & patterns ~ Sable, Isabella, Blue & Tan, English Cream, Chocolate & Tan, Red, Black & Tan
Longhairs can't carry smooth or wire.
Smooths can carry longhair, but cannot carry wire.
Wire can carry smooth and longhair.
Genetics is a struggle and partly because the way we use the language.
For each trait, a dog has a pair of genes, one donated by each parent.
A dominant trait is manifested if present in only one of the genes.
A recessive trait is manifested only if present in each gene of the pair.
For Coat type the Hierarchy goes like this:
(W)ire Absolutely Dominant
(S)mooth Dominant only to Long
(L)ong Recessive to Wire or Smooth
Dogs with a twin pair( W/W, S/S, L/L ) can only offer their own coat type to any progeny.
Since (W) is absolutely dominant, a W/W dog will only produce wires irrespective of what their mate offers.
Canada, the UK and other kennel clubs dis-allow cross-breeding of Coat types.
Two W/S dogs could produce smooth puppies. Smooth is recessive only in the presence of the Wire gene.
A W/S dog and a W/L dog could produce a S/L pair of genes, in other words, a Smooth puppy.
Two W/L dogs could likewise produce longhair pups.
Wire breeders(show) have a difficult time setting a uniform and correct coat because of the issues of incomplete dominance and the
recessive nature of the other coat types.