I can't help you with the coffee flavored eliquid. I like to drink my coffee. I have gotten a couple of coffee flavored eliquids from VapeWild that I liked, either as free samples or as part of a sample pack, but I had to scrub my tank after I used their Frappapow - it darkened the glass on my Evod Glass to the point that I could not see the eliquid level at all. The taste was good, though. Their Tiramisu is good, I reordered that a couple of times. I have not had it recently and cannot remember how dark the eliquid was, but it was not too terribly hard on the Kanger single coils that I like in the Evod Glass.
What I can tell you is that I have had my Nautilus Mini for about a week and a half, and I am still using the 1.8 ohm coil that came preinstalled. The most I ever got from a Kanger coil, whether single or dual, was maybe 5 or 6 days, if I was lucky. Usually I only get 2-3 days. The nice thing about the Kanger single coils, for me, is that I can clean them and get a few more uses from each coil before I trash them. I am not sure how cleaning the Nautilus coils will go, but right now I am very happy with the coil life on the Nautilus Mini.
Right now, I have Mt. Baker's Pretzlemint Bark in the Nautilus -chocolate, peppermint and pretzel flavor. Before that, when I first got the Nautilus, I was using Mt. Baker's Monkey Mousse - chocolate and banana. I tend to vape sweet dessert flavors, along with bakery, creams and custards. Not the best for coil life. So far, I have been using 50/50 pg/vg eliquids in the Nautilus. It will be interesting to see how it handles 70 vg/30 pg - some of the vendors that I order from do not offer 50/50, and start out at 70 vg/30 pg.
I hope your Mom enjoys her Nautilus Mini as much as my daughter and I are enjoying ours. You are a fantastic son to take care of Mom this way.