I have 3 kids and my youngest of 15mos has eczema (he can thank me for this!). We battled it rough while he was an infant, but once we started using Triamcinalone (prescription,low dose steroid ointment that comes in a tub like aquaphor) along with aquaphor he immediately started to heal and sleep better! We use it minimally and only as neeeded. Ointment based medicines seems to work better for us just b/c they hold in the moisture better than creams.
If she has irritation along the diaper line, first I would make sure you're changing her frequently enough (the wetness could be doing this). Switching diapers and seeing what happens is a good thought-is it possible to do cloth? Maybe they are just too tight or she is sweaty/wet in that area? Not sure if you mean diaper line around tummy or legs. Once you've got control of the eczema, you could lube the area in between diaper changes w/ eucerine or aquaphor-this may provide enough of a buffer.
Instead of dreft, try arm and hammer free and clear-I switched to this from using all free and clear years ago because it is cheaper and the same-no perfumes and dyes. The dreft company really markets towards being a "baby detergent" but not only is Arm and hammer much cheaper, it is exactly the same!
Also, stay away from the aveeno cleanser as it still may irritate her sensitive skin. Cleanse with cetaphyl cleanser for hand washing and bathing her (Walmart has a generic brand that is a third of the cost-the equate cleanser and it is on the beauty aisle). Even just a good rinse is helpful to get the salts rinsed off her body which can irritate her skin. You can accomplish this in the a.m. when she wakes up by using a warm, wet wash cloth and blotting the areas of concern (I had to do this for my baby head to toe until we got control of his eczema). And be sure to lube her up w/ eucerine (walmart also has a generic eucerine) or aquaphor immediately after bath-pat dry then lube, lube, lube everywhere! We even lube our son's head-looks a little greasy right after but it keeps his scalp moist and no dry skin there!
Try oatmeal baths if her skin is really dry-put oats in a blender and then add the powder to her warm bath water (just make it a no hair wash night that night!). This is similar to the aveeno oatmeal bath stuff you can buy.
Also, something else to do that really works for us is make sure she is getting yogurt (we like the yo-baby organic, but they do make organic lowfat too) and/or organic cottage cheese (which has all the good bacteria that yogurt has-regular cottage cheese does not!). Acidophilis, bifidum, and those types of "good" bacteria are very beneficial to the skin. Also, plenty of high quality fruit-dark berries-again organic is best, my kids even enjoy the frozen berries thawed out. All the vit c is good for skin too (and has a natural antihisthamine which helps with itching-when I have serious bougts w/ eczema I up my vit c intake by double or triple and it really helps-you just pee out what your body doesn't need so it is safe).
Speaking of food-have you ruled out food allergy-try eliminating one thing at a time from her diet for 2wks and see if she improves (thought if you use the med I mentioned she will improve). Common triggers are dairy, wheat, eggs-but if she has been fine with them up until now it may not be the cause. Something to think about.
Hope this helps. I sure do understand and feel for you and your daughter-both from the perspective of having it myself and also trying to help my little guy as well. Your daughter may be old enough for benedryl/zyrtec if itchies get real bad but check w/ ped first.
All the best and happy healing. -A.