She's referring to how computers, tablets and phones emit blue light which stimulates your brain and keeps you awake, resulting in insomnia.
Not... really resulting in insomnia. It does, supposedly, make it harder to sleep for (as per Taw's mom) about a half hour, iirc, but it's not really any better at
keeping you awake than any other stimulating activity, so far as I'm aware. 'Bout as easy to power through the night reading a particularly gripping book or watching TV (Well, listening to a TV for 8 hours straight would personally just make me want to kill people, but... eh.) as it is mucking about on the computer.
And it's not just computers. It's books, TV, activity in general... basically anything. There's a period after mental stimulation during which it's harder to sleep (Surprise! That's a secret to
freaking no one.). Harder doesn't mean impossible, and it varies by person (those fuckers that can just conk out, may they burn in hell for all eternity after I rip their means of doing so from their brains, are what they are. The bastards.),
and I'm fairly sure you can acclimate to it after a while (I go to sleep easier after using a computer than I did a decade ago, ferex. Not saying much 'cause it's still 30+ min on the average goddamn regardless but whatever.), but... yeah.
Though when it comes right down to it it's a half bloody hour. That's not much missed sleep, if it's any missed sleep at all. Just go to sleep a bit earlier if you got stuff to do in the morning.
E: All that said, I've never actually used f.lux before. This... this is nice.