It's unlikely you did anything wrong. If you did she would have (or should have) mentioned it. She didn't. On the contrary, she did the opposite. She told you she enjoyed the date a few times and then went completely silent. So this isn't on you.
It's hard to say exactly why she's ghosting you, but in the end the reason doesn't matter. The fact she can't tell you she changed her mind about seeing you again (for whatever reason) means she's not worth your time. You don't just leave someone hanging like this. It's dishonest and disrespectful even if it seems easier or less painful to reject someone like that.
Rejections aren't easy to get and not certainly not great to give, yet if things change for whatever reason you should do come out with it. No doubt you could have handled it if she told you the date way great but she got back with her ex or it was too soon or she got swept up in the moment, or whatever reason she has for not wanting that second date. You might not have liked it, but at least you knew where you stood directly. You know now too, but you first had to wonder a few days and are doubting yourself. Don't.
Again, this isn't about you. This is about her changing her mind and not able to tell you this. Her loss, no need to make it yours by questioning your actions. Even if you did do something wrong (which seems unlikely) if she can't tell you, then you can't do anything about it. So don't fret about it and see this as her problem. Move on and maybe if she does get back in touch you can tell her how shitty this move was. Don't waste your time telling her now though, it will only make you look bad or like you can't handle a rejection. You can handle it so just move on instead.