Live ball apeal or not

[canump]

Hey guys & gals
Had a fellow ump call me the other day about a play he had. He was BU for thi game.
R1 on 2nd, R2 on 1st with 1 out. Batter hits hard line drive that bounces off the fence between F9 & F8 in right feild. R1 is runnuing with injured leg, ( occured earlier in game but no subs available as whole team was not there yet due to traffic) (they had 9 players so game started on time). R1 stops at 3rd, R2 is running hard and rounds 2nd heading for 3rd but completely missed 2nd as she was watching the ball, halfway to 3rd she realizes that R1 was standing on the base, she stops & reverses direction back to 2nd. F4 is standing on the outfielfd side of second about 2 steps off. Nobody yelled at that time that runner missed 2nd and F4 caught the throw turned, stepped and at the same time of stepping on 2nd tossed the ball to F1. No verbal or anything about the missed bag as F4 had no idea as her back was to 2nd. R1 makes it back just as F1 yells "Umpy she missed 2nd and that was apeal live"
BU disalowed apeal as no indication came from F4 that she was appealing either verbal or by her actions.
I informed him that he could have considered it as an accidental appeal but he strongly says that the feilder is still required to indicate somehow that he/she is making an appeal.
Any feed back would be appreciated.
Thanks
Wid.