Yeah 16 weeks is young to even try to use the bands on them LOL...I feel your pain. They're too bz moving around, hardly stays still.
It takes lots of patience on your part, lots of praises (leave the no's out) & yummy treats & eventually, they'll get used to it. Just like hair & teeth brushing, they hate it @ 1st but will tolerate (LOL) it.
Not sure what kind of bands you're using, but the smallest band (1/4" the ones usu on handmade bows) is the easiest to put on bc it only goes around the hair 2-3 x's (depending on how much hair they have on their head).
Put her on your lap or wherever she tends to not be so energizer bunny like, but really, the BEST time is when she's tuckered out & sleepy.
Or you can temporarily wrap a thick towel around her like a bumper, give her a treat & praise her, make it fun & do it that way.