It is possible she didn't know to count out the change in change. It amazes me these days how many young people can not make change unless the register tells them the amount.
In the old days, you counted back the change from the price of the item, and the amount the customer gave you. That was the only way to do it.
(Boy, do I sound like my parents! Never thought I'd see the day!) 
Actually, the best way to do it is to count UP. For example, if you paid for a $17.33 item with a $20, it would take you much longer to subtract 17.33 from 20 (dealing with carrying numbers and whatnot) than to do this: 33 to 100 is an increase of 67. So 67 cents. Then add the two dollars from 18 to 20. The total back is $2.67.
Making change was in our fourth-grade math curriculum back when dinosaurs roamed the earth without calculators. We learned to count up cents from the purchase amount to the nearest 25, 50 or 75 cent mark, then add whatever number of quarters to get to the next dollar, then add subsequent dollars.
Total is $6.22. Purchaser gives you $10. That's 3 cents to get to $3.25, then 3 quarters to get to $7, and another $3 makes $10. Change is $3.78. Way faster than subtracting, for me at least. Letting the register do it is faster still, although sometimes it forgets to make the calculation, and I'm glad I have my 40-year-old change-making skillz.
Topic? Oh, yeah. At the store where I work (neighborhood convenience store, part of a regional chain) we gladly give out change, whether it's breaking a dollar bill for the pay phone or a roll of quarters for laundry. We have ONE bank in town, its hours are limited (9-3, later on Friday, and Saturday mornings), so if the change machine at the laundromat is broken and it's 6 p.m. on a Tuesday, we're the only change game in town, especially for folks without wheels.
A bigger hassle than the customer wanting change is the employee wanting to cash his/her check -- yes, we are authorized to cash one another's paychecks from the till. It's a great convenience that I as an employee appreciate, but it becomes a hassle when the full-timers with the $300-and-up paychecks come in to get and cash their checks right after the registers have been skimmed for a bank deposit! Deposits are done at relatively random intervals (may be at 10, 1 and 4:25 one day, 9:45, 2:30 and 6:15 the next), so it's not like the check cashers are doing it on purpose. Just one of those weird ironic coincidence things -- like the car always breaking down on payday or it always raining on laundry day.
