What exactly doesn't go smoothly when she shifts the front? If she doesn't understand that at the same time the front is shifted that the rear must be shifted two or three cogs to get the correct next ratio, then that might be why she's 30 meters behind all of a sudden. And if on that 3x she's going from the large to the smallest ring in one shift, intentionally or unintentionally, well that's an issue too and maybe a simple adjustment.
Might be the old stuff is worn out and can't be adjusted. But since it's a 3x, you really need to determine if those lower ratios are needed. If they are, then maybe 10 speed Tiagra 4700 with a 3x crank will be a good upgrade. And they still make it so it can be all new stuff instead of used that you hope works. And certainly less expensive than the 105 R7000 that will only be 2x and not give the low ratios that might be needed.
If you can describe the actual issues with the front shifting that you say is happening, then maybe there is a fix for that. Is your bike a size that she can ride and you ride hers to compare?
Last edited by Iride01; 09-25-22 at 09:41 AM.