If you are feeding Land O Lakes, then she's getting really good milk replacer. I've heard of eggs in milk...I even got desperate once and tried it...and it didn't work. And, I've heard of Karo syrup...but haven't tried that. Are the scours really bad? If they are, and you can get hold of it, give the calf a shot of nuflor and banamine/supressor. When a calf gets down weak with scours, pneumonia can take over. They are prescription meds, btw.
Also, tho I've not used them, I've read a lot of people here use scour boluses and swear by them. I've used the spectam pig scour stuff and I guess it works as well as the next.
The thing is, the calf is 3 weeks old, and around here we would hold our breath until a calf was 2 weeks old. If it didn't scour by 2 weeks, we rejoiced...if it was scouring and still alive at 2-3 weeks, we rejoiced. After 2 weeks one would rarely scour. Also, the calves we were raising were holstein bull babies bought from the auction barn...so they may or may not have had colostrum and were exposed to all kinds of garbage.
You calf was born on your property and given colostrum. If you've got a vet that will give you the time of day about a baby calf, call him/her. And see if you can't snag a script for nuflor and banamine.
If not, give the calf the LA200...what the heck...you've tried everything else...
Again, this only what I would do.
Alice