Every chicken keeper knows that moment when a seemingly perfect brooder turns into a mystery novel. You've done everything right: fresh water, starter crumble, heat lamp dialed in. Your other chicks are zipping around like tiny feathered race cars. But Mint, your sapphire gem, just sits there. She's eating. She's drinking. She's also vibrating like a cell phone on silent and showing zero interest in the whole "standing and walking" thing. That's not lazy. That's a red flag with feathers attached.
Let's get practical, because panicking doesn't help anyone, least of all Mint. The fact that she's eating and drinking is good. That means she's not immediately shutting down from starvation or dehydration. But a two-week-old chick who can't walk far and prefers lying down? That's a symptom worth dropping everything for. The purring or vibrating sensation you described isn't a happy chirp, it can signal weakness, pain, or a metabolic issue. Vitamin deficiencies are possible, especially with fast-growing breeds like sapphire gems, but so are things like coccidiosis, leg injuries, or early signs of Marek's disease. The problem is that multiple conditions start the same way. You can't treat what you don't know.
Your plan to hit Tractor Supply is sensible, but here's what we'd add: grab a bottle of poultry-specific electrolyte and vitamin supplement, preferably one with vitamin B complex and vitamin E. Selenium and vitamin E deficiency is a classic cause of the wobbles and general weakness in young chicks. While you're there, also pick up a small syringe (no needle) for dosing liquids, because a chick that's weak may not drink enough on her own. Separate her in a warm, quiet space with a low-sided dish of supplemented water. Don't force her to stand. Let her rest. But also keep a close eye on her droppings, any sign of blood or unusual color means you need a vet, not just a feed store.
What we'd tell any reader who brought us Mint's story is this: you did the right thing by separating her and paying attention. Too many people brush off a quiet chick as "just the calm one" and lose it overnight. Trust that gut feeling that something is fowl brewing. For now, supportive care and a targeted vitamin boost are your best first move. But if she doesn't improve significantly in 12-24 hours, or if she gets worse, find a poultry vet with that same urgency you'd show a sick dog. Chickens don't show weakness until they're in real trouble, so when you see the sign, you move.