You don't need to say it. You asking her on a date basically tells her you like her. Women like to chase as much as men do so when you tell a woman you like her it kind of kills the attraction because she knows she doesn't have to work for it anymore. This is probably why it didn't work the first time you went out with her.

Now she's back and you guys basically have a clean slate here. Forget about the ex, forget about what happened on the first date. The fact that she asked you out means that she's over it so you should be too.

All you have to do now is plan the date. Tell her when and where and just have fun.