Yes, he noticed.

When they got to the car Nigel pushed her firmly but not violent in any way and said. "We can't have you breaking the dresscode now, can we?"
"Sorry, what?" Sarah responded.
"I saw your thong when you hugged your father and there was not a pair in the packade. But I can make an exception this time, however they can not be seen."

With that he reached under Sarah's skirt and ripped the thong off. Sarah's heart was pounding, she felt so powerless to do anything and could only hope that there wasn't any more consequences for wearing the thong. But she wasn't so lucky for Nigel had already started pushing the torn thong upp Sarah's pussy.

It didn't hurt her since they weren't that much fabric, but it wasn't comfortable either since both her pussy and the fabric was dry.

It took Nigel some effort getting the thong completely hidden in Sarah's pussy but when he was done he gave her a quick pat on her butt and said. "Now that we are ready to go, please hopp in." And with that he let go of her and opened the back door.
Sarah got in and Nigel joined her right after. Nigel closed the door after him and gave the driver a look who started the car and drove away from Sarah's home.