I made clean install of Windows 7, left some space unallocated on SSD and during subsequent Mint 18.3 install with default "Alongside" option did not got Windows in grub boot menu.
I write this mainly duplicate because the solution was simpler than in other questions I found here, see my answer.
Just ran command below in Mint and Windows 7 was added to grub menu along with Memtest btw.
sudo update-grub
Thanks for the tip goes to more lengthy:
Windows 7 not shown in GRUB menu, will not boot via BIOS, after Linux Mint clean install
Some developer, please add this to installer.