The Invitations

It was the day after Christmas. CJ looked out her window to a fresh layer of snow. The tiny snowflakes twinkled in her eyes.
CJ jumped out of her bed and into the kitchen. Her mother was busy making breakfast when she said "good morning."
CJ reached for the phone to dial her friend, Ashton's number.
"Hello," said a groggy voice on the other end.
"Ashton look outside," said CJ excitedly. She could just envision her friend's eyes lighting up.
"Wow!" cried Ashton. She seemed to have woken up more.
CJ invited Ashton over to try out her new sled at noon.
At breakfast, CJ's mom asked if she had gotten any RSVP's to her their party.
"No, I haven't. Ashton was supposed to send the invitation's last week. I'll ask her when I see her this afternoon."
After getting suited up, CJ headed for the slopes. Ashton was waiting on the bench.
The girls climbed the hill and raced back down it.
As they slowed at the bottom, Ashton screamed, "We should go sledding at the New Years party.
CJ agreed. "Did you send the invitations yet?"
"Yes, I put them in the mail yesterday.
After sledding, the girls went back to CJ's house for hot cocoa.
Ashton asked if CJ had gotten any RSVP's for their party.
"How can if you didn't send the invitations?"

How did CJ know that Ashton didn't send the invitations?