I am getting an old laptop for my cousin to use for shopping online and excel spreadsheet. which is pretty much what she will only use it for. it has no OS but was wondering if it is better to install windows 10 or windows 7, from a performance perspective?
8 yr old Netbook with a very low end CPU? Skip it, no amount of money savings would make that system worth buying. If someone gave that to me for free I'd think they did not like me. You can get a Core i3 or i5 laptop for about $100-150 for a system in good shape. Lenovo T420/420s specifically are great in that price range. And they should have Win 7 OEM license key on them so easy to install OS and get a valid license. For a smaller system, Lenovo X201 is good.
Cheap solid state drive if they don't have one will make a huge speed difference also.