Rear wheel off center?

I’ve been working on my son’s MTB, a 20” Cannondale Quick, and recently noticed how far off-center the rear wheel is. I don’t see any obvious bends or cracks in the frame. Any ideas on what it could be and how I might fix it? Or is it SOL? The rear axle is properly seated. He has been riding it plenty, but I just put a new shifter and derailer on which really accentuated the problem as the chain rubs against the guard when it’s on the granny gear. The picture makes it look like the wheel is crooked, I think it runs straight, just off center.Any helpful advice is appreciated!