Your wife made a good decision by buying it from Amazon. Amazon is very strict about customer service. If 1 of their vendors gets a number of bad comments or reviews they come down hard on that vendor. Vendors are genuinely worried about losing their store on Amazon, so they bend over backwards to make things right. Congratulate her for me.
Your wife’s decision is doubly good, because dual shaft motors, like the 1 used for the Y axis, are somewhat hard to locate.
As to what you might have done wrong, well, as I said, forcing an axis to move when its stepper motor is energized is not a good idea. I did misspeak a little in my last post when I said not to move the axis with the power on. That’s not strictly true. What matters is whether a stepper is energized. The system will keep a motor energized to hold the axis in a specific location. It’s part of the accuracy of the system. However, there are times when a system is powered on but the motors are not energized. At those times it is not a problem to move the axes manually. The way you tell is by applying just a little pressure. If you feel resistance, back off, don’t force it.
So, what can you do while you wait for the replacement motor? A couple of things:
As part of the diagnostic process you can unplug the wire from the Y axis motor and disconnect the motor from the 2 shaft couplers. This is something you will have to do anyway, so no biggie. Then, try spinning the shaft. Is it super stiff? Does it move easily? I’ll address what to do if it spins easily in a bit but, if it is stiff, it’s further confirmation that the motor is toast.
The 2nd thing you can do is check for mechanical issues with the Y axis without the motor. Try moving the X axis crossbar from front to back to front. Does it move easily? If not, it could be a sign that your issue is actually mechanical. This is especially true if the Y stepper does move easily. It could be that the motor is actually fine. It might be that, somehow, the Y axis dual belt system got out of whack, causing the axis to ‘rack’, leading to binding. The way to check is to, once again, plug the wire back into the Y stepper and try sending it a command (without it be connected to the axis). If it spins well, that would tend to again suggest mechanical problems.
I think it may be possible that 1 or both Y axis belts may have been too loose, leading to 1 of the belts getting out of sync with its twin: i.e. racking.