Was I in the wrong?

So my 3 year old niece was doing one of those books where you trace a letter and then try on your own and was melting down because her lower case Ns didn’t math the one in the book (they still were a n but didn’t look perfect like the texted one.) I asked what was wrong and she told me that hers aren’t good enough and don’t look like the one in the books. I said “oh honey that’s okay. They looks like Ns to me, as long as you try your very best you will never fail. Remember it’s okay to stop what you’re doing and breathe and calm down when you’re feeling sad and angry at the same time and then try again once you’re ready.” She did what I said with a smile on her face and did a perfect n. My sister in law bitched me out and said “ do you ever tell my daughter that as long as she try’s she won’t fail. Failure is serious and no child of mine will ever fail.”