Rinsworth

If the build is just for school and such, you should consider using an SSD rather than, or alongside, the HDD. It makes life a lot easier, and will help considerably more than a better CPU or GPU.
 
Also, if she's running Windows 10, the computer will probably need 8GB of RAM to work well, or it could bottleneck the rest of the components.

This really isn't that true. Crucial is a great brand, and although the Samsungs do last somewhat longer, it isn't worth the extra cash for the extra time. 
 
Also the speeds are very close. It isn't a SATA2 HDD vs an NVMe SSD. 
 
The Samsung has speeds 
Max Sequential Read Up to 540 MBps Max Sequential Write Up to 520 MBps The Crucial has speeds of
Max Sequential Read Up to 530 MBps Max Sequential Write Up to 510 MBps

There is going to be a pretty good bottleneck, and 3D modeling isn't all GPU power. The PC itself isn't going to run very well, as long as the CPU is bottlenecking the GPU that much. Also, 2009 was using PCI Express 2.1, rather than the current PCIe 4.0 (actually 3.0). Not only is the CPU bottlenecking the GPU, but the PCI Lanes themselves!

There is going to be a pretty good bottleneck, and 3D modeling isn't all GPU power. The PC itself isn't going to run very well, as long as the CPU is bottlenecking the GPU that much. Also, 2009 was using PCI Express 2.1, rather than the current PCIe 4.0 (actually 3.0). Not only is the CPU bottlenecking the GPU, but the PCI Lanes themselves!

This really isn't that true. Crucial is a great brand, and although the Samsungs do last somewhat longer, it isn't worth the extra cash for the extra time. 
 
Also the speeds are very close. It isn't a SATA2 HDD vs an NVMe SSD. 
 
The Samsung has speeds 
Max Sequential Read Up to 540 MBps Max Sequential Write Up to 520 MBps The Crucial has speeds of
Max Sequential Read Up to 530 MBps Max Sequential Write Up to 510 MBps

Hot damn I made a mistake. 3.0 "It's 3.0." Gah I'm tired sorry.

Going back to the subject
PCPartPicker part list: https://pcpartpicker.com/list/T8sfgL
Price breakdown by merchant: https://pcpartpicker.com/list/T8sfgL/by_merchant/ 
 
CPU: AMD - Ryzen 5 1600 3.2GHz 6-Core Processor  ($195.88 @ OutletPC) 
Motherboard: *ASRock - AB350M-HDV Micro ATX AM4 Motherboard  ($67.98 @ Newegg) 
Memory: *G.Skill - Ripjaws V Series 8GB (1 x 8GB) DDR4-2800 Memory  ($58.99 @ Newegg) 
Storage: *SanDisk - SSD PLUS 240GB 2.5" Solid State Drive  ($75.58 @ Amazon) 
Storage: *Hitachi - Deskstar 7K2000 2TB 3.5" 7200RPM Internal Hard Drive  ($58.99 @ Amazon) 
Video Card: *MSI - GeForce GTX 1060 6GB 6GB GT OCV1 Video Card  ($234.99 @ Newegg) 
Case: Corsair - Carbide SPEC-M2 MicroATX Mid Tower Case  ($54.99 @ Corsair) 
Power Supply: *Corsair - TXM Gold 550W 80+ Gold Certified Semi-Modular ATX Power Supply  ($62.98 @ Newegg) 
Total: $810.38
Prices include shipping, taxes, and discounts when available
*Lowest price parts chosen from parametric criteria
Generated by PCPartPicker 2017-06-12 11:40 EDT-0400
 
https://pcpartpicker.com/list/T8sfgL 
 
This should be good enough for streaming. Choosing a Ryzen CPU seems better than getting a 500 USD Xeon and then cheaping out on everything else. Dedicating the extra 2 cores to streaming is good enough for early streamers. If you want to replace the GTX 1060 with an RX 580, it's a bit extra, but should be fine. 

It might be a bit overkill to do 4 on one side of the case. Remember that other components need air as well. As long as there is good airflow, it should work, and everything should be fine. Also, (just a suggestion) radiators should be pushing air outside of the case. Having the main intake of air pull in hot air from the CPU or GPU isn't too good of an idea.

If they've had them for a year, there is going to be slowdowns, but not *that* much. 
 
Samsungs, at least in my experience, are guarenteed to be good, only a bit more expensive.

This really isn't that true. Crucial is a great brand, and although the Samsungs do last somewhat longer, it isn't worth the extra cash for the extra time. 
 
Also the speeds are very close. It isn't a SATA2 HDD vs an NVMe SSD. 
 
The Samsung has speeds 
Max Sequential Read Up to 540 MBps Max Sequential Write Up to 520 MBps The Crucial has speeds of
Max Sequential Read Up to 530 MBps Max Sequential Write Up to 510 MBps