I actually don't personally care for the pico but I do recommend (the mod) because so many folks like it. I actually my first MTL kit was an Aspire Zelos mod with a Nautilus 2 tank. I think the Melo III would be fine for your significant other though, if she likes "small" DL kits, it would probably be the right type of resistance for her, I'd think. Etc.
So if I'm understanding you correctly I guess she'd potentially like the tank with the caveat that (as I recall) it is a pretty small tank, although I think filling is no big hassle or chore.
If someone asks for a small starter setup, I will often say that the pico is liked by MANY. It's not my cup of tea for a variety of reasons, but it sounds like I don't vape like your GF and I've been at this a while enough to know what I like, which sometimes can be pricy.
There's nothing WRONG with the pico and lots of people swear by them. I just didn't have the greatest experience with mine, but that doesn't mean I don't "like'" it in general, it's an excellent MOD certainly (and kit, for many folks) and the price and size are great.
That's pretty much all I have to say on the subject. If you don't mind an internal battery (I don't generally recommend them that much though I have a few) I might suggest a tarot nano kit, it has kind of "restricted" DL hit and the battery life isn't bad. It surely is small and cute. And, as with any internal battery mod, it has a shelf life. With vaping going where it is I'd be a lot more likely to recommend the pico simply for the fact that it's one of the few mods of its size to have a removable battery and TC capability. Etc.
Hope that helps.
Anna