A knight asked to my party to go to the Radiant Heart because Lady Vanya want something.
She wasn't there.
Have I to wait for some days? Or clua her?

For lady Vanya to appear you should have:
1- Have a non-evil protagonist
2- Have killed firkraag
3- Have a reputation of 20
4- One week should have passed since you killed Firkraag
Do your party satisfy all these conditions?
If not, the messenger should not have appeared at all unless your reputation is dropped below 20 between the time the knight came and the time you went to meet Vanya.

CG
Done
ok
I am not sure if a week is passed, I overwrite the savegame. But the messenger approached me and I went immediatly to the radiant heart.

Have you searched everywhere inside the Radiant Heart (she should be near the back door)? I just checked and everything seems correct. If she is not there, rest for a few days to make sure than one week has passed. If she doesn't appear again, then let me know. Your reputation is still 20, right?

Everythings is fine.
two days later I met her.