I've owned four NEF/H&R singleshots or Survivor guns. ALL had the SB1 receiver, so I'm very glad I got rid of them!
To be clear about this, I like the NEF line-up of guns and their barrel exchange program, but now that I understand how the barrels are exchanged, I realize I had the wrong receivers!
If I may suggest, get something in a good rifle caliber for your granddaughter like a .243 W, 7mm-08 R, or .30-30 (good starter calibers), and send that "SB2 type-receiver" gun back to NEF to have a shotgun barrel installed. The real key to NEF's barrel exchange program is using the stronger rifle-type SB2 receiver as the chasis of your NEF longgun, and then you can outfit every centerfire offering on it BUT NOT THE OTHER WAY AROUND! The SB1 receiver can only be outfitted with other shotshell barrels, but no rifle barrels. So its imperative to start with the SB2 receiver to build a collection of barrels around.
Two exceptions; Only the Sportster rimfire action can be used for the .22 and .17 rimfire rounds - PERIOD! And only the 10-gauge receiver is used for the 10 gauge barrels. A shooter can get extra (smaller gauge) shotgun barrels for his 10 guage gun, but not visa versa (don't ask me why).
From what I've seen of the Rossi's, I'm NOT impressed - knowing the NEF's offer a much better looking and handling product, and a more diverse list of choices. Also, I'd trust the NEF's service reputation more too - being made in the USA.
If your granddaughter is older and has been shooting for a while, NEF also offers rifles in the .270 Win, .280 Rem, .308 Win and .30/06 as well as the others listed above amd many others.
Try looking around this site to answer any questions you might have; www.hr1871.com