Loli Ymir is from the distant past. What the concept of PATHS and The Coordinate are presumably about is how the lives of ALL Eldians originate from Loli Ymir.
Loli Ymir is, according to Chapter 120, a servant and a slave to those of Royal Blood possessing the Founding Titan (Coordinate).
There's a lot of speculation and mystery behind "how" Ymir and her powers, all 9 titans, came to be - a miracle of God, a girl who made a deal with the Devil, a girl who touched the source of all life, etc.
But with Chapter 120 in view, it can be inferred that Ymir has transcended the physical realm and only resides in the PATHS dimension to serve the Royal bloodline wielding the Founding Titan.