You're printing PLA on plain glass with some glue or just so without anything ?
I print almost always on plain glass with a thin layer of 3Dlack (kind of hairspray)
Small pieces get off without any struggle.
Only larger surfaces give sometime some issues, but
- designing bottom layer with a small chamfer/fillet may help
- using a blade from a cutter to get under the piece for some mm and then driving the chisel between the blade and the glass does the job.
Force is always parallel with the glass surface.