@scochranoc 
she will be able to smell you in the house, and hear you come in, however much you creep. Unless she is deaf/has hearing loss of course.
What I have done with my fosters with severe separation anxiety (I do a "light" version with pups) is every day I have taken them to get the mail, the mail box is at the end of our driveway, which is pretty long, so walking up there and back takes a few minutes.
Before I take them, I say "just going to get the mail" after a few days or weeks (depending on how anxious) I say "just going to get the mail, back in a minute" and go out of the door and sit on the bench outside for ten seconds.
Then I come back in and say "I`m back" and greet them happily but calmly, and not over the top. Gradually I increase the time on the bench until its five minutes, then I actually do go and get the mail.
The idea behind doing it this way is that they can smell me outside the door, and hear me, so they know that although I am out of sight I am still there, and they already know what "going to get the mail" entails, ie its quick, still on our property, something I do everyday, and something I always return from.
When I do actually start getting the mail, they can`t see or smell me, but again already know I will be back soon as they used to accompany me, so know exactly what I am doing and where I am going.
Then I start taking them in the car to the gas station/shop and just park for five minutes, do not actually shop or put gas in the car, same "just going to the gas station" and then again "just going to the gas station, back in a minute". So now its getting them used to hearing the car leave too, and again something they know as they have been accompanying you, and you can slowly increase the time you are out.
Then gradually you phase out the "just going to..." and just stick with the "back in a minute". So wherever you go now they trust you that "back in a minute" means just that, and they have seen time and time again that you will return, and all the while you work on confidence building, and your bond with them grows, so that they know that they can rely on you.
You can also leave a kong/puzzle game for them whilst out, personally I prefer puzzles, but whatever works best.
One of the very respected behaviourists I worked closely with is very anti not making a fuss of your dog when you return, and having seen and tried it both ways many times I completely agree.
The reasoning is that your dog is always happy to see you, they love you and want to be with you, and so in their minds you should be happy to see them too.
Coming in and not greeting them is not "normal" in their world, and when you are asking them to learn to cope with something "abnormal" like leaving them alone, keeping as many things normal and sensible to them as possible helps hugely. They understand much better, and so will be much more willing to give you the benefit of the doubt and trust you that leaving isn`t such a big deal.
For a happy, loved dog or pup, rarely any reason they would ever want to be away from their family. Its a bit of a foreign concept to dogs. They can in time learn to tolerate it, and with some dogs enjoy the activities they do whilst away from you, but their preference will always be to be with you.
By not ignoring them when you return, you are solidifying in their minds that they are a loved, valued family member, and that you would always rather be with them but sometimes you can`t, and that helps them feel secure. So, they are valued and loved so you will return and not leave them behind, iyswim.
I am not in the UK, and more and more behaviourists where I am are following the not ignoring advice now, but as always, your pup your choice. I am aware this goes against a lot of conventional advice given, but I have found it infinitely more successful at curing separation anxiety in even the most severe fosters I have had.