I would not worry, and I would not bother with an evaluation until age 2.
My daughter at 16mo had no spoken words (but several signs). Maybe mama, I can't recall for sure. Around 16mo is when her first few words started... "shoes" was first lol... but that was it for a good while.
Around 20mo or so she hit her 'explosion'. She had close to 100 signs, and started adding 3 new spoken words every single day!!!
She's now 3.5yo, won't shut up, and is one of the most articulate kids you'll meet. She's actually quite advanced, in terms of pronounciation, vocabulary, and usage.
I honestly believe that most kids who do EI don't really need it. Sure, there's no "harm" because it's kind of fun, but it's... well, it's creating a culture where it's believed that it's needed much more than it is, and creating a lack of trust in our children's natural development, and a skewed idea of what is "normal".
You hear so many stories of "no words at 16mo, so we started EI, and at 20mo she started talking so much, therefore the EI worked". But you hear just as many stories of "no words at 16mo, we did nothing else extra, and at 20mo she started talking so much." In other words, I think that much of the time, the kids just start talking because they were going to talk around then anyway, EI or no EI.
16-18mo is still well within the normal range for talking. Later than most? Sure. But that's why it's a RANGE. And it sounds like you're doing everything you "should be" doing. She's able to make lots of different sounds and understands the concepts of words. Those are the two things she needs, and she's got them, so now it's just a matter of her putting it all together in her own time. I honestly think you just need to relax and trust her natural development, which seems totally normal and on-track. Speech is an instinctive human skill, it's extraordinarily rare for a young human to not develop it completely self-driven (barring of course issues like autism, but that certainly does not seem to be the case here).
I even think that speech intervention for older kids is over-used. Do some kids need it? Probably. But most issues being dealt with in speech therapy are really quite normal and folks will grow out of them eventually... you see very few adults who still have those articulation issues, and not because they all had speech therapy.
My older son was a very early talker, so it was odd for us when DD was so "late". But we never worried. My younger brother did not say a WORD until he was THREE. By that age, my parents were indeed starting to worry. Then one morning he came into the kitchen and said "hi mom, could I have some breakfast please?" We figure he was just waiting until he had the WHOLE THING figured out and didn't want to fiddle-faddle around with babytalk and incomplete sentences... And now as a very successful adult he's still very much a perfectionist.
