Since the Mama is likely not able to spend a ton of money on detergents and utilities and might not even have her own washer and dryer, I'd go with flats.
Our charity cloth gifts are always flats, so that the baby never really outgrows them, and they never give the Mama a headache with the laundry.
Flats really, really, really, really don't have that much of a learning curve. My son's caregivers have had an easier time with flats than with AIOs ... it's just a matter of what you're familiar with.
You also don't know what size/shape the baby is, and what it might be sensitive to.
I was a very broke Mama when I started out, and started with flats, less because of the cost of entry than the ease of care and the fact that he wouldn't outgrow them. Nobody ever had a problem with them. When I "upgraded" to BG pockets, BGEs, Grovia AIOs, Best Bottoms, Babykicks fitteds and pockets, gCloth inserts, and a few others I always had to quit because of the cost of washing & drying, and the difficulties getting other things clean. Flats wash in one cycle and hang dry in a few hours, if that's what's necessary.
I guess to put it briefly ... You may see that prefolds or flats have a big learning curve, but to a person with very limited means, washing AIOs or pockets and dealing with their fit and many other possible problems is a very very big learning curve.
I'd get this:
18 Green Mountain Diapers size small flats, unbleached
... $36 This will get through a day plus in the infant stage, and 2 days in toddler land.
And, since she might not have money in future for adding to her stash, a heavy duty One-Size cover, in snaps, that fits most babies ...
I recommend Flips
they worked best for us pad folding with flats ... 3 for $42. Make sure 2 are light colors that don't show under light clothes (I tend to donate noodle, butternut, and clementine).
And 7 inexpensive size small doublers
Those things with shipping add up to $100.
When you wrap it, you can pad fold a flat in the covers, and add a doubler to one.
Then you could add a note ... "I'm not sure if you're familiar with flat diapers; they are a favorite of many mamas because they grow with your baby, they are easy to wash and dry, and they last forever. Maybe you already know what a Snappi is, and how to fold flats ... if not here are some references ..."
I just can't stress enough how sending AIOs or pockets could be a complete nightmare for the mama. When I diverged from flats I spent a ton of money on diapers that didn't end up working. And washed any diaper but flats, our utility bills went up $20 a month (and when I was super broke, that's 7 days of food for me).
I'd also ask for the "intro to cloth" pamphlet from Green Mountain Diapers, and include it with your gift. It's amazing and she can then call GMD with questions.
Good luck choosing and kudos for giving such a great gift.