Poor wee mite, Ok best friendly brands are micofiber clothes and water (seriously you can clean anything with water and a mico fiber cloth) if Something is really really stuck steam it and then micro fiber it.
it certainly could be air fresheners. particularly the type that spary a mist into the air. which would also look fairly generalised,
Ok, next get on phone to mum (or email might be better) and have a proper compare and contrast! Done a bit for you
Fabric Softener?
Cleaning (how often, with what, what perfume etc)
Carpet (if you have not steam cleaned before it could be something from befor you owned the house)
Do you have pot plants does mum what type
Go room by room one thing at a time and see if you can find the differences. If you can cut out the differences, deep clean, See if DD skins clears if so you know somewhere in the differences you have found the cause. Add one back in at a time per week.
Ie, if different plants, put 1 plant back in a week later (or sooner if there is a problem obvsiouly) take plant 1 back out, put plant 2 in.
It may not be one thing, but maybe a combination of things together.
For example with me I can use the shampoo, conditioner and the hair spray of the same brand at the same time but NOT the styling foam, or I can use the styling foam with the shampoo but not the conditioner. or I can use the hair spray with the foam and thats ok! Weird Hey.
Also thinking back about it, is the eczama clearing when you take DD upstairs for a nap, and then reflaring when you bring her back down stairs? If so it could be more contact allergy than eczama (sorry)
One last thing, it could be pestisides, ie if Mum shops at the local organic market she might have pestiside free fruit, or if Mum shops at a different super market to you she may have different pestisides on fruit.
Pm if you want to chat with an adult with eczama