AnnasDad - I think in those situations (limited practice time, limited one-on-one instruction, etc.), timing is your best avenue to achieving any semblance of consistency or success. For this scenario, I was going to equate timing with sequence - but making contact just requires getting the bat on the ball. You can do this with poor mechanics and sequence (it would be an ugly swing, but you can still make contact). You can't do this with poor timing. Being on time is a key starting point - you can improve weak contact by swinging harder, improve the sequence by teaching them small things like hip rotation, and finishing the swing. Whereas with poor timing, swinging harder will often just get you a nice "woosh" sound when you swing and miss.
cbullard - To get back to your OP (and after seeing the video you added), to my novice eye, I don't see any extension issue. I'm guessing whoever saw her in real time noticed the way her wrist hinged at the very end of her follow through, and thought the way the bat came back around was an indication of poor extension. When you slow the video down, to me it looks like she's clearly extending.
cbullard - To get back to your OP (and after seeing the video you added), to my novice eye, I don't see any extension issue. I'm guessing whoever saw her in real time noticed the way her wrist hinged at the very end of her follow through, and thought the way the bat came back around was an indication of poor extension. When you slow the video down, to me it looks like she's clearly extending.