That's a tough call. I have a friend that I always hoped would get into sewing (and join me in my madness). Her mother bought her an inexpensive machine at Walmart, and she had so much trouble with it she completely gave up on sewing. Even I had trouble with it.
All you can do is read the reviews on that particular machine, bear in mind that Walmart has a generous return policy, and wait to see how it plays out. If the niece really starts to like sewing, she can upgrade without too much having been spent (the machine you bought is much more on Amazon), and if she gives up on it, not a lot has been invested.
You didn't do the wrong thing...
