Mine free range and stay safe because my dogs roam freely with the chickens. It wouldn't surprise me if yours has been safe for the same reason.
I wouldn't get more chickens unless you just want more chickens. She's been alone so long that it's likely to be a pretty difficult adjustment. It's not at all like adding a dog or cat. Chickens can be cannibalistic dinosaurs. If you decide you want to keep chickens, you will want a proper coop (or section of the garage) and you will want to raise new ones where they can see and hear each other but are physically separated til the chicks are her size. If you decide to get just one or two that are her size, you still want to separate them in this way, probably for at least a week. In addition, new chickens should be quarantined for at least a month, which means keeping them far enough apart that airborne diseases cannot be passed. Even then, quarantine is no guarantee of not bringing in a disease. Chickens can be carriers of several chicken diseases and never show symptoms.
That being said, chickens are great to have in the backyard.... this is a chicken-enabler website, of course....
The comb turning red tells me you are likely to find an egg soon. If it were me I'd probably put a cardboard box with some rags in it next to her cage, with a golf ball in there if you have one. They normally lay only during daylight hours. Hay and straw are great nesting material but you can't exactly buy a small bag. Don't buy cedar chips, commonly sold as rabbit litter. I'd also take out a search around the yard -- they like anywhere more or less hidden, under a bush or a pile of wood, etc.
How great of you to rescue her, and how lucky for her. If she was an easter present, you got doubly lucky, because they are usually roosters.