The first thing I always look for whenever I see screenshots of champions is the speed on their selected champion, and I don't like the looks of that speed on Visix there. +30 speed is much too low if you want to start tackling some of the later content.
Does she have boots with speed as the primary stat? If not, then swap them out now for a pair that does, even if the rest of the stats are crap. A champion cannot do anything if they never cycle around to their abilities. On average, most of your champions should be around the 180 to 200 speed in total to push on. If you don't have any boots with speed as the primary stat, then you need to start running some dungeons more.
With regards to the boss itself, I think it will be similar to the potion keeps in that the lower levels will likely be achievable by early/mid game players, but the rewards will probably not be much. In other words, I do think it'll be both easy and hard, and I suspect with your current roster you should be able to tackle the initial levels quite well