Willow has always been a fast learner.
When Giles' tut-tutted about the sites she looked up, Willow understood he meant don't get caught.
When he told her magic could be dangerous, he meant take it slowly.
When he pursed his lips as she repaired the Buffybot, it was just his way of saying that without her, they'd all be lost.
Which is why, when she's had time to analyze Giles' harsh words, she's no longer angry. It must be hard to admit that only she was capable of doing the one thing he wanted to do. So, she forgives him.