I wouldn't.
I leave mine with their flock. Reproductive disorders are not contagious. Even if it did turn out to be LL, the whole flock's been exposed for a long time.
If I had to take a wild guess - Some type of reproductive problem. Cancer, Salpingitis, etc. Could be an avian virus like Leukosis. The only way to get answers is if you lose her and have a necropsy.
Sounds like she is slowing down, but for me...normal poop, no crop problems, still lays an egg once in a while - not her time yet.
That said. Only you can really be the one that can gauge how well she is and make that call.