I personally have strong feelings about letting cats roam outdoors, and my intent is not to offend those who feel differently about it...so please, just accept that this is my opinion, and I certainly do respect that others may share a different sentiment on the issue.
I feel that as pets, cats should be strictly indoors. There are so many risks involved in letting a cat roam freely around the outside of our homes, and in our neighborhoods. I do understand that many feel that letting their cats outside for a few hours a day (even under supervision) enhances their quality of life, which for many cats, this may be true. Cats are curious creatures, and the great outdoors provides wonderful opportunities for exercise and stimulation...and allows them to exercise their instincts as predators as well. I can't argue against any of these points, as I do understand that once some cats get a taste of the outdoor experience, it can be a difficult inclination to break, and that most owners who allow their cats outdoors, do so with their pet's best interest at heart.
However, these are dangerous times for our feline friends, and really, there is no farm, yard, or neighborhood safe enough. There will be strangers who abuse or kid-nap our cats, feed our cats a diet (also with good intentions) that may be less than desirable, children who "pick on" the neighborhood kitty, and creeps who leave out that dish of antifreeze, to "teach us a lesson" about allowing the cat to trapse through their garden. There will be plants growing in yards that poison our cats, cars to crawl up underneath, and nails/glass to step on. There will be cars that will either purposefully or nonpurposefully hit our cats (I've seen this more times than you could imagine), and diseased rodents and birds to kill, making our pets sick or diseased themselves. Perhaps one of the greatest enemies our outdoor cats face are other outdoor cats...cats are by nature, very territorial...and it is almost inevitable that our pets will come in contact with a stray/feral looking to defend it's territory. Fights happen, biting and scratching occur...and here again, a serious risk of disease contracted through bite wounds, saliva, and scratch wounds...FeLV and FIV being a serious threat to your cat's well-being and health.
Neko is a beautiful cat...and no doubt, enjoys the wonders of the great outdoors. I realize that she may yearn to be out there...but she will continue getting attacked, either by the current cat, or possibly another. This is a horrible health hazard to your baby...not just the injuries but possible diseases she could contract through her wounds.
There are ways to create a stimulating environment for your cat inside...and inside only. Cat trees placed by a window so she can "bird watch", scheduled play times, and providing cat grass are just a few ways. She may be miffed at you for not allowing her to go out, but with time, she'll adjust, and you'll have the comfort of knowing that she won't fall prey to any of the risks I mentioned.
Again, please don't take offense. I realize that you love Neko, and want what is best for her. And I would encourage you to not take action against the "offending" outdoor kitty...he/she is doing what is instinctually made to do. The choice is ultimately up to you, but given Neko's current circumstances, I would definitely consider keeping her indoors for good.