Cloud storage is fine for sharing and warm or cold backup but less than ideal for hot files.
And you always need an Internet connection which is not always available or robust.
She's a student, 1 TB Onedrive plus access to Office suite, ~$1.50 a month.
https://products.office.com/en-us/university
Alternately, and likely more convenient, expand her storage.
IIRC you got her a 2015 15' Retina MacBook Pro.
It has an SDXC slot.
You can get an all in one solution like a JetDrive
https://www.amazon.com/s/?_encoding=UTF8&camp=1789&creative=390957&field-keywords=Transcend%20jetdrive%20lite&linkCode=ur2&tag=9to503-20&url=search-alias%3Daps&linkId=2GC6JD6EO7PLJKQR
or use a Micro SD adaptor plus micro SD card.
https://www.amazon.com/aluminum-microSD-Adapter-MacBook-onwards/dp/B012F8ALBC/ref=sr_1_9?ie=UTF8&qid=1515676900&sr=8-9&keywords=Nifty+minidrive
https://www.amazon.com/Samsung-microSDXC-Adapter-MB-MC256GA-EU/dp/B06XFS5657/ref=sr_1_4?s=pc&ie=UTF8&qid=1515677341&sr=1-4&keywords=micro+sd+card&refinements=p_n_feature_two_browse-bin%3A13203835011
Micro SD vs JetDrive cost is basically a wash but with an adapter you can just pick up more cards for additional capacity or use what you already have even swap files with others by swapping cards.
Were it me, I'd take advantage of the student discount on Office 365 and in addition do the micro SD adapter.
NOTE: When buying SD cards only buy name brands. If 256GB averages $125 and you see one for $50 stay away.
There is no shortage of retailers who take cheap and slow low capacity cards and slap a label on indicating multiples of the capacity they are actually capable of.
EDIT: Had some coffee. Those SDXC adaptors also work on Air's although depending on the model it may or may not be interchangeable with the MacBook. The iPad requirement is even more reason to consider Office 365, gives you access to the mobile versions of Office apps.
At $1.50 a month it's practically free.