I remember the first time I was with a man who didn't even want to have intercourse right away. He just wanted to please me and make me cum. Was wierd, never happened before. But then again I was also taught that women are there for the man's pleasure and since the wind blew and I got off it was no biggie...
Then as I became more experienced I realized that there are times when either party cant get off if they are nervous, if they have issues in their head, etc and it is no big deal. So DONT LIE, just say that you are happy that she came and that is enough for you. You are REALLY into her and want to delay your climax for as long as possible because it makes it so much better when you do cum.
If you lie then she wont feel compelled to work extra hard in the next round.
*hint* *hint*
Payback is ALWAYS better if you set it up this way when you are with a normal chick and not one that has to file her nails or asks you not to muss her hair while you fuck her lifeless corpse.