So sorry for your loss... I've been there too.
Did the vet have an idea what caused him to colic? Most often it's just one horse who happens to be prone to impaction or didn't drink enough, etc but it's always a good idea to take a close look at what they are eating & be sure there's not a problem with any of your hay or feed, or that they aren't getting into questionable weeds...just consider everything. I've had several colics over the years that resulted in surgery and have one mare who is very prone to colic, so I have become ultra vigilant about what they are fed & have access to.
Hope your little mare is able to have a buddy again - and depending on her personality, she may or may not like her new companion at first so you might need to have a way to let them get acquainted safely.
Jan