Yeah, but I think I would go with the Mini if going that route, instead of the Nano. Here's why, the overhang from the Mini on the iStick 20w wouldn't really be that much. Plus the fact that the Subtank goes through juice faster, the Nano only holding 3ml of juice versus the 4.5ml in the Mini, you would be refilling the Nano quite often unless she's a light vaper. Also, the Mini comes with the RBA option, so you could utilize that too if you wanted. Although, the stock OCC coils in the Subtank look simple to rebuild, just by looking at them and from the videos... I haven't actually rebuilt one yet. I don't know... to each his own... plus the Nano is quite a bit cheaper. As easy as it is to rebuild these coils, maybe I wouldn't ever use the RBA attachment... time will tell.
I've never used an Atlantis so I can't say which I would prefer. I've always been a little partial to Kangertech from the T2s, Evods, Protanks, to Aerotanks and now Subtanks. I've just always had good luck with them. If someone gives me an Atlantis to try someday, I might just like it better and make the switch... who knows? I just know that I'm satisfied enough with the Subtank that I'm not really "looking" for a new one. Although I wasn't looking to replace our Aerotanks either, it was all the good reviews that made me want to try it I guess. Now that I've tried the wife's, I feel like I want one for myself. I have a feeling it will be my go-to tank and cause me to retire a lot of equipment.