I think it sounds like this garage sale lady just clipped off the babies (unrooted) from her plants and stuck them in pots?
I assume you uppotted them in your new container -- did they have tender fleshy white roots or did they look like hard tentacles?
If my suspicion is correct, then they took a while to actually grow soil-roots in your pot. The babies set down roots much easier and quicker/stronger when they are still umbilically attached to the mother plant (the process is a lot like strawberry plants).
It's possible the conditions you had this baby in wasn't the ideal for growing roots -- lower humidity, not quite sufficient water, too much sun, etc.
So if your plant is growing new leaves and shoots now, I'm guessing it's finally established and you should see it take off. It's a foliage plant so give it 1/4 or 1/2 strength fertilizer that is higher in N (first number). Or you could do what I do for my favorite plants and water it with any leftover beverage (coffee, milk, juice) diluted with filtered water (swish to rinse your cup/mug/glass and water)
...I can't grow spider plants -- I think I mentioned before somewhere that ever since I brought my first kitten home, spider plants were doomed. Last and FINAL time I tried, one kitty was teetering on the edge of a deep octagonal aquarium to reach the hanging spider plant babies and managed to push aside the glass 1/2 cover and nearly fell in WITH the AQUARIUM LIGHT.
The spider plant was evicted and sent away to my Mom's soon after.
(... But...but! My babies and I didn't DO anything! We were just HANGING AROUND!!!)