Calming bands work by basically bringing the dog awareness of the mouth/muzzle area, and can be good for vocal dogs because they are often very tense around the mouth.
I've found so far they either work like magic or they don't have much effect (although sometimes you need to try different widths of elastic as just changing the width can make all the difference - you can make your own by buying nicker or garter elastic and making a figure of 8 with it, one loop around their neck like a collar and the other loop over the muzzle).
I use a Mekuti one with Zorro and it's brilliant on him, really effective (with him I use it for general anxiety rather than for vocalisation). One thing I've learned from Zorro is that it really helps to use it pre-emptively - his anxiety directly relates to how tense his lower back and legs are, so every morning I have a feel and if he's tightened up overnight, I'll pop his calming band on, and he then never escalates his behaviour. But I also do a fair amount of TTouch on him and try and keep the house nice and calm, no raised voices, no mega exciting games etc as it tends to just raise his anxiety levels overall. I don't know how well a calming band would work if that were the only thing you were doing but let me know how you get on.
It sounds as though Lexi could do with some general bodywork as well though as it sounds like she's fairly stressy. Does she sleep well when the other dogs are around or is she just on edge all the time? Sleep can be a major factor in dogs' stress levels, just think what you feel like if you've not slept properly for a few nights on the trot - alot more likely to over-react to things, and dogs need alot more sleep than us... The other dogs will be hearing all the same stuff as her but not feeling stressed so they're not bothering to react to it.
Have you tried a bodywrap on her at all? If she's feeling generally insecure then that could help, also gently massaging her ears and doing little one and a quarter circles around her muzzle if she'll let you.
PM me if you want any help