Hi YourHand, sorry to hear you are struggling with SA as well.
I'd recommend the DAP diffuser, rather than the spray. Lurcherboy started to connect the smell of the DAP spray on his bed with me leaving, so we had to stop using it. 
As well as DAP, I use Dorwest Herbs Scullcap and Valerian tablets and top them up with a dose of valerian compound if he seems particularly on edge. I forgot to give him the pills for two days in a row last week and he howled like a wolf on the second day, so I do think they're having some effect.
I've found he doesn't really go for kongs. In fact he hasn't touched them at all since I bought his treat dispensing ball, even though I always put both down for him.
Also, only give her a kong/treat toy when you leave and remove it when you return. This will help her to associate you leaving with positive things happening and over time will counter-condition her current association with feeling anxiety/distress when you leave. If you leave the toy down when you are around, it doesn't have the same effect.
Have you tried desensitising her to your leaving routine? Doing things like picking up your keys then sitting down. Doing your hair, putting your coat on and picking up your handbag then watching tv. Basically, whatever your normal 'leaving the house routine' is, break it down and desensitise her to each step. Doing all this randomly, but frequently, gradually building up to doing the whole routine, but without leaving the house will help her to relax if she is picking up on signals that you are about to leave her.
Same with heading for the exit and actually going out of the exit. Work up to it very slowly, moving towards the exit a little way, but not leaving, then closer and closer, then hand on the door handle, then open the door, then stand in the doorway, then go through, then shut the door for a second, then gradually start extending the length of time you are on the other side before coming back in. You need to do each step lots of times and if she starts to look at all stressed or worried, go back a couple of steps until she is coping before moving on again.
You can also make sure she spends periods of time sitting in a different room to you with the door closed, so that she starts to relax when left on her own in a room. You can use a kong or treat toy for this, so that she makes positive associations with 'alone time'.
Do you usually have the tv or radio on when you are home at all? If so, perhaps try leaving it on when you go out, so there's some normal background noise rather than sudden silence when you close the door.
I presume she wasn't left alone by your mum, which could be what's behind this. It might also be that, after you brought her home, she started fretting when you left her sooner than you realise, but was perhaps just stressed and whiny at first, then worked her way up to the chewing/destructive behaviour.
The good news is that, as it's new behaviour, it shouldn't take very long to sort out. You just need to reaffirm the good associations she had with being at home and being relaxed when you left her that she had before she went to your mum's house.