The 7 signal

We needed 180 to meld. It was the second round of play. My partner discarded a seven which to me meant that she had 2 sevens. I discarded my 2 sevens and by the time I picked the pack there were 5 sevens and I thought she had 2 of them. When I laid down the 5 sevens my partner didn't have any. She said she wouldn't keep one in her hand because she needed 180 and a seven wouldn't do her any good. In my regular weekly game this wouldn't be acceptable in this situation. Of course, there are times when a seven could be discarded and not be a signal (avoiding the pack to be picked, 2 cards left, etc). This group I was playing with insisted I was wrong, and that a seven played early in the game should not be construed as a signal.