I am about 90% certain that if her job required her to transport kids, they would require at least a 3 year clean driving record and that would have been requested and reviewed as part of a background check.
If her job does not require her to drive, then the most an employer can require is, "do you have a reliable means of transport to work?" Beyond that they cannot dictate.
I think it is highly likely that they are asking for a driver's license as a shortcut to filling out her I-9 form, which requires a form of primary identification. There are alternatives.
In her shoes, I would call the HR rep and first clarify if I am expected to drive on the job. If no, I would inquire about why they are asking for driver's license. If for purposes of identification, ask what other documents are available as an alternative (there is a standardized handout you can simply Google online that will tell you this too.) If they have another reason for requesting this and it is a legit reason, discuss her plans for obtaining her driver's license.
Worst case scenario, driving is a part of the job requirement and she's screwed, but that seems very very unlikely if they did not background check her driving record.