You know what? My first thought was "Hmmm, bloody unhappy kiddo verses spending $100 on some clothes that make her comfortable".
Seems to me that getting her clothes that she can live in would be the first priority. Sorry if this isn't what you want to hear. I know how hard it is to spend money like that. We live on a fixed income and we're raising grand kids.
I ALWAYS google items like this that I am searching for by adding "special needs" on the end of the sentence.
Like this:
Larger onsies for special needs kids
I got sight after sight after sight.
They all cost right around $20. So I suggest you rethink your decision about spending $20 on onsies for her. She claws herself until she bleeds mom. What's more important? Her comfort or having that money for something else? Please see if one of these sights has just what you need them perhaps go on some donation web sight where you can ask friends and family to help out.
Several of my friends have done this and share it on GB. They got money donated by even total strangers. To buy books for their classroom, to take their kid who had a long illness but is better now on a good fun vacation, and more.
I know you have bills to pay just like the rest of us do but spending money on something this important isn't a waste of money. She needs them.
http://www.essentialwhites.com/t-g_tube_care.aspx
http://whiteletters.hubpages.com/hub/Clothing-for-Special...
Up to 6T
http://www.amazon.com/Toddler-Sleeveless-Onesie-Bodysuit-...
Some adaptive clothing can be a good substitute too. Mant moms have posted they have school ager kids that have feeding tubes and having onsies to fit them is important.
http://www.feedingtubeawareness.com/AdaptiveClothing.html
http://www.tanniandanni.com/kidsclothing/poppervests.htm
How to make your own
http://somethingsewspecial.blogspot.com/2010/06/sew-big-k...
This idea might be really simple. If she has underwear that she likes to wear over a diaper then finding simple soft tees could be the answer. Simply sew the bottom of the tee to the inside of the waistband of the undies. Soft, no inside seam, and you can do them for any size.
http://www.iammommahearmeroar.net/2010/04/always-tuck-me-...
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My last thought on the question. I work in a clothing store in a dance studio. I feel a LOT of materials that leotards are made of. The softest and most long lasting are the stretchy velvet ones. They wash and dry and last for years. I wash ours on warm and dry on delicate or perma press.
I don't get any that have a sheen to them, the metalic look. That stuff is scratchy on the inside to me.
GK and Under Armor are awesome brands. BUT Discount Dance is going to have clearance leotards for as little at $4.99 sometimes.
Cut the crotch open and add velcro dots so they don't rub her or have someone add a strip of snaps.