I had terrible problems with itchy skin when I was in my thirties. I'd had exzema as a child, too.
I had tests; they put about 12 different allergens on each arm. After they scraped me off the ceiling, they assessed my swollen blistering arms and said I was 'multiply allergic'. No kidding.

All kinds of things were tried - exclusion diets, different soaps, different washing powder, goats' milk - you name it, we tried it.
Eventually I was in such a state I was hospitalised. Drugged to calm the screaming nerve ends, and swathed in bandages slathered with soothing pastes - which also stopped my fingers reaching the broken abused skin.
Icthopaste bandages - ahhhhhhhhh.
They kept me in for three weeks to let the skin heal. It was explained to me that once you are sensitized, any eruption can give rise to increased sensitivity elsewhere - so if I got a sore patch and scratched it, I could end up with flare-ups elsewhere even though there'd been no external trigger there.
I am absolutely fine now, and live and work amongst all kinds of dust, dirt, hay seeds, animal hair, etc, etc. I can even wear homespun wool against my skin

I can't give you a 100% definite explanation but I can tell you some things that I observed and some that I believe to be true.
When very sensitive, I found it helpful to do the following
- no soap at all, use unguentum merck to wash, don't towel but let it dry on your body
- at the outset I found oilatum emollient in the bath helped; after a while I became sensitized to that too - so nothing at all in the bath water except the ungy merck
- when the skin got so itchy I couldn't stop scratching, the icthopaste bandages were wonderful. In the absence of them, or where they couldn't be applied, coal tar and calomine was the best - your chemist can make you some up
- to suppress sudden flare-ups, I'd use a prescription steroid ointment, which was presented in coal tar base - but I'd be very frugal with it and not use it widely over my body because of the longterm issues with steroidal creams
- i used non-biological baby sensitive washing powder on any clothing or bedding which would be close to my skin - Filletti was the best
- try to keep the dust and unseen house-mites down in the house; I had covers on the mattress and pillows to reduce the contact with house mite / bed bugs
- get your skin exposed to the sun (or these days, a safe sunlamp is maybe better) whenever possible - obviously without overdoing it. The specialist who hospitalised me said he would send all his patients to the South of France to swim in the sea and dry in the sun twice daily for three weeks if the NHS would pay for it. (Again, the sun wasn't thought to be dangerous itself in those days.)
- change all next-to-the-skin clothes daily; dust from dead skin builds up in them extra fast when you have these problems
I can't tell you for sure why I got better but factors I believe relevant include:
- reduced stress - changed job, much less negative stress at work
- very prompt treatment of small itchy areas to preclude a more widespread flare-up
- pay attention to which fabrics cause and which suppress irritation and be brutal with your wardrobe - and be prepared to put covers on any chairs you use, including your office chair
- I never did wear makeup anyway, but I would certainly have stopped doing so
- moved more than 2 miles away from busy (motorway class) roads
- switched to spring water supply, not mains water
- a more outdoors way of life - more gardening and long walks with the dogs when I was still working in an office, now of course I am outdoors more than inside

- changed diet to eat more organic and fresh meat and veg, far less processed food and avoiding additives like colourants
Oh - and somewhere in the recovery period, I gave up smoking.
The top things that improved the health of my skin, in order of their impact in my view, were:
- changing to spring water, coming off mains water - Exmoor water on your skin does more good than any ointments, and then some
- using unguentum merck instead of soap (I can use simple soap etc now, but stayed with ungy merck for years)
- moving away from traffic pollution and giving up smoking
- changing job to a less stressful environment
- changes in diet and lifestyle to eat more fresh food and get more sun on my skin
And the only other thing I can think of to mention is this. At one point, after the hospitalisation but when I would still get flare-ups if I wasn't very careful, I cleared a large area of our garden of nettles. When you have skin allergies like I did, nettle rash is nothing, and it was a lovely sunny day so I did the job in shorts and sleeveless vest. That night I couldn't sleep, my legs were raging. It didn't itch, not a bit, and I wouldn't quite call it pain, but whatever it was, it kept me awake all that night and for quite a lot of the next few nights.
After that, I was super-sensitive to nettles and had to cover my legs when out walking, wear gloves when weeding if I might come into contact, even very slight contact, with nettles.
It has occurred to me that the reaction of the body to the total overload with the nettle toxins may have paradoxically desensitized the skin to other irritants.
Please do tell your daughter to contact me directly if she would like to know more about my experiences.