Not following a treat...

Because JRT are famously stubborn/their 'own dogs'/'independent thinkers' it may take loooooong time penny to drop what you are after. Or it may well be that she knows but she has come to conclusion that despite your best effort, it ain't worth of doing.
So either you are into long haul training until she will follow your demands or you might as well forget it and do what she likes to do. They are thoroughly entertaining dogs but maybe it is a best to allow the dog to think to itself and problem solve the given instructions by other means than treats. Do you need to teach that trick?
Try something else that she might REALLY really want and would do anything to get hold of it...a toy?...something smelly(rub something smelly on it) or noisy?
I was told a game here, one that my terriers would like to trial...'ball in the sock'...and they LOVE it! But their way of playing is ragging it. But it has now turned into very desirable toy too. Although the first version of it is now seen its best and is ready for 're-socking'...when ever I take it into my hand, I have the full attention of the dogs and their beady eyes follow the toy guessing what it about to happen.
Maybe something like that would work with your terrier too...just play with it first to make it hers

 

And to add...my terriers don't tend to do things for sake of a treat anymore neither. That phase that they would 'work for it' was short, when they were still young pups. Now it has to be something much more exciting..food is food and that's it.