If you're single then no you're not in the wrong. If you're seeing her then depending on where you're at then it could be wrong. Normally when I'm seeing someone I stay faithful and don't see anyone else. Others see things differently and are fine with seeing multiple people until they become an item and exclusive. If you have told her you want to be with her and she said yes and on that basis is planning to come over and see her family and you then yes you are in the wrong.
If you're single there is no much she can do. She may be disappointed but you're well within your rights to do what you want. However, if you've led her on to the point where she has come over and have now gone and arranged a date with someone else then that's a bit bad yeah. However, i'd still go through with the other date judging by your OP.
1) you are single
2) she is coming over but she said to see her family
3) this date may end up evolving into something more - it may end up in just friendship
4) if you like both then why not try your luck with both?
I'd say misleading someone is the wrong bit so if you've done that then yes to a degree it is wrong but don't beat yourself up over it. Just next time you speak, see both of them make your mind up and go with your instinct.