Damping Off

With that degree of stem stretch, I think the light was either too far away or not on for long enough. If that happens you can stick some stakes (chopsticks work if you have them) to act as a support and wait for the stem to thicken up and support itself, or you can bury the stem up to just below the cotyledons (that first set of tiny, small round leaves that appear after it ditches the shell casing). It'll take about five days for leaf growth to start up again from my experience, but that's because the buried section of the stem is busy sprouting new roots. After that she'll growing a bit more slowly at first, but then catch up. and just be behind schedule by about a week. It's a great way to save leggy sprouts and not worry about the extra hassle of supporting them for a few weeks till they can stand on their own. You don't need to do anything other than literally add in the dirt; though I'd recommend avoiding an entire repotting if possible. Those tap roots shoot out hard and quick, and if they get damaged during the transfer then you'll still have her kicking back into gear in a week but there's a chance that the root damage will cause her to get stunted.