Lurcherboy did this when we lost our old girl. It was a huge shock, because he's a really laid back lad and nothing ever bothers him, but he grieved terribly and I came back to a very rude note from my neighbours one morning after attending one of my dc's school assembly. Apparently he started doing it straight after she died, but we had no idea. (We are in a semi too and our neighbours are retired with no kids or pets. Fortunately they were very understanding once I went to see them and explain that firstly, we had no idea he'd started doing it and secondly, we were working hard to help him learn to cope on his own and could they please let us know if/when they hear him, because it would help with his training programme.)
I did lots of things to help him - more walks in different places, keeping him busy with search, hide and seek and retrieve games and generally trying to wear him out as much as possible. I had a distinct advantage in being a sahm though, so was able to stop going out and build up the time he was left gradually. Kongs didn't work for him, he either didn't get them or couldn't be bothered to put the effort into emptying them. I thought it was grief stopping him wanting to eat at first, but discovered that he preferred treat balls, buster cubes and kong wobblers etc and they kept him busy for a while. Another thing I did was use a dictaphone to record him, so I had some idea of just how much howling he was doing and how he was progressing once we started working on it with him.
We had decided not to get another dog when we lost our old girl, but had to rethink when we saw how distressed Lurcherboy was. We were pretty sure getting another dog would work because it was Isolation Distress, rather than Separation Anxiety (as he was fine as long as somebody, anybody, was with him, rather than needing a specific person to be there). We lost our girl in April and picked up Pip early August. By then Lurcherboy was already coping with being left for an hour and a half, but it was hard work and often three steps forwards, two steps back. Once we brought Pip home Lurcherboy was cured overnight - despite not actually liking the annoying puppy - unfortunately with his bad start and being very poorly when we first got him Pip ended up with true Separation Anxiety in a big way. Two years down the line, I still can't leave him home along for longer than an hour - and an hour is pushing it sometimes. I often wonder if Lurcherboy would have just continued to improve had we not got another dog and anyway, he could go longer by the time we got Pip than Pip can after two years of hard work with him. I love Pip to pieces and would never be without him but to say it has been extremely hard and had a major impact on my life and freedom would be the understatement of the century. 
Is there any chance you could find some dog-daycare locally until you get another dog or could she perhaps go and 'visit' someone on the days you work? It's going to be very hard to work training her out of it if you're not around, as the basis of the training is gradual desensitisation and teaching to self-settle and they need to be kept under threshold the whole time. Failing that, it's worth trying an extra long walk before you leave and then perhaps two visits from someone during the day, given that your dd is home at 3.00 anyway. I would also try a variety of treat dispensing toys and either rotate them or give her a couple at a time. Teaching her to search for hidden treats is another good game to keep her occupied.
The best books I've found to help me get my head around ID/SA are Don't Leave Me, by Nicole Wilde and Treating Separation Anxiety in Dogs, by Malena Demartini-Price.