OS choice for Core 2 Duo PC

[minibarex]

Hi. I am planning to build a pc with some spare parts of mine, that I will give to my sister (she only does basic computer things, not gaming etc.)
I was wondering if should choose Windows 7 or Windows 10 as the OS.
Specs:
Intel 945P motherboard

Intel Core 2 Duo E7600 ark: http://ark.intel.com/products/41495
3.07 ghz, 3mb cache, 1066 MHz fsb.
4 gb DDR 2 667 MHz ram

Nvidia GeForce GT 630 4GB DDR3 PCIe 2.0

350 W PSU

1TB 7200 RPM HDD

I was wondering if windows 10 would run smoothly on this pc. I don't expect it to run super fast or anything, just that it will run FINE, (no stuttering, no constant 100% CPU usage, not ridiculous loading times for browser etc.)

I already have Windows 10, and I would rather not buy another copy of Windows 7.

Thanks in advance for all help.

 

[clutchc]

Win10 is probably the better choice. Win7 is going to have support suspended in 2018. The requirements for Win 10 is here: https://www.microsoft.com/en-us/windows/windows-10-specifications
Your old system meets the requirements, so you should be fine. On average, Win10 does everything a bit faster than Win7 no matter the system.