Sean, may I suggest the help of a professional seamstress who can adjust the clothing to make them comfortable and maybe hide the seams with a patch of softer cloth to make them lie flat and smooth and be covered by extra soft fabric which will not induce pain on your daughter.
In addition maybe the website you bought the socks from can guide you where to buy pants, leggings or tights from. But most probably the best bet is to find a good seamstress and a good fabric store so that you can buy fabric that is very, very soft. If you can’t find fabric soft enough, try taking a very soft sheet like 600 count cotton and make leggings or pants from that.