I am lookin for some type of companion for this horse to make her the happiest she can be here. Another horse is not an option.
Are you sure another horse is out of the question? Perhaps you contact the nearest rescue for an older horse with no maintenance? As has been mentioned, two companions are better, so your ‘main horse’ can go off property without causing the aging ones distress at being ‘alone’.
Older rescues, or rescues who can’t be ridden, can be hard to place. But can also be very kind and rewarding, and good babysitters for another, younger and more fussy horse. And a great added experience for your daughter, as well.
I hope you’ll continue to keep an open mind as you go forward, and not assume too much about anything without more information. New territory is new learning for all of us.