Just my personal take, but I think vaporizers are awful! If I'm smoking flower (buds), I'm rolling it or using a glass pipe. I never understood the allure of flower vaporizers. But, honestly, I hardly ever smoke flower these days. Too messy, too smelly, just not needed. THC oil cartridges in vape pens is absolutely the direction she should go. First, it's not smoke, so it's much less damaging to your lungs. Second, it has nowhere near the 'consume the room'-smell that smoking bud does. And they taste amazing! I don't like ones with flavors added as I like the taste of herb. But they make the oil cartridges in every flavor you can imagine. Some are just the THC itself (well, terpenes) but they are labeled like they taste (kind of like people describe flavors from wine), but some (especially black market ones) add flavor to them. And lastly, they are just so **** easy and convenient to pull out, take a quick rip and put away. You can basically do it anywhere and no one even knows. That's probably what I love most about oil vs buds. Though I do both as I went most of my life with only bud.
As to the sleep question, like everyone above said, indica is the key. Think of it as "In-Da-Couch" as most are more the "duhhhhhhhhh" buzz which helps with sleep. I use sativa or hybrid oil during the day (as they generally give you a more alert and energetic buzz and, more importantly, you don't crash when they wear off) and indica at night. My favorite nighttime oil is Gorilla Glue #4 (GG4). Agree 100% with what El said, she'll want to blaze a bit before she goes to bed and not hit it right as she turns the lights out. Many people get a rush or even a paranoid feeling in that first hour. It's when you start coming down that it makes you sleepy.
And, lastly, I don't like edibles at all (tinctures, gummies, whatever). It's a completely different feeling when you eat THC vs when you smoke it, in my opinion. Never been a fan of edibles, although I'll eat them if there. LOL
Get that lady a vape pen with an indica cartridge and she'll be a happy camper! ;-)