What I would do is go to any sheet metal shop and get some pieces of sheet metal. Use children's adhesive putty (which can easily be removed), or very small pieces of double sided mounting tape (which you can buy at any hardware store) to mount pieces of sheet metal over the glass in the area you're working. Now, use your hair dryer set on HI to heat the paint in a corner and slide a putty knife between the two wooden parts that are painted together. As the area warms up, the paint will soften and you'll be better able to slide a putty knife in and separate the window from the frame.
Metal is a good conductor of heat, so it'll allow the heat to dissipate laterally along the sheet metal, and that will prevent you're cracking the glass if one part of the glass is wanting to expand and the rest doesn't.
Also, inspect the joint between the window and frame very closely. Latex paints in North America are made predominantly from one of two different kinds of plastic; polyvinyl acetate and polymethyl methacrylate. (So far as I know, no paints use binders that are a mixture of the two different kinds of plastic, but I suppose it's possible to do that, although I don't see any real need for doing that.)
You probably know polyvinyl acetate better as "white wood glue", and polymethyl methacrylate better as Plexiglas or Lucite or Perspex (if made by Rohm & Haas, Dupont or ICI, respectively). Polyvinyl acetate is predominantly used to make PVA or "general purpose" latex primers and budget priced interior and exterior latex paints. Polymethyl methacrylate is used to make better quality interior and exterior latex paints and specialty primers like concrete primers that are intended to be applied over fresh concrete, which is highly alkaline.
ONE of the many problems with Polyvinyl Acetate paints is that adhesion is simply a difficult property to engineer out of the PVA molecule (which is why it makes a good glue). Even when fully dried, PVA retains a slight tackiness, whether it's fully dried PVA glue or fully dried PVA paint. What I'm saying is that it may be that the windows aren't actually painted together at all, but that the paint on the window is simply sticking to the paint on the frame (and that happens all the time with people who use inexpensive paints to paint windows and doors and such).
(When I was in university, I often read laying in my bed in the residence I was staying at. When I would rest my head against the wall, I found that my hair would always end up sticking to the paint on the wall. That was a mystery to me until I bought an apartment block and started learning more about paint. I soon found out that the reason my hair was sticking to the paint was because the moisture from my scalp was softening the PVA paint on the walls, and that combined with the paint's being naturally sticky, even when dry, is what was causing my hair to stick.)
So, take a bright light and have a real good look at the light reflection off the joint between window and frame and see if it looks like a single continuous coat of paint between the two, or separate coats of paint on each. If it's a single coat of paint, they're painted together, and I'd try heating the paint to soften it. However, if it more looks like the two coats of paint are sticking to each other, then I'd try using an artist's paint brush to paint water onto the joint you want to separate. That's cuz yet another problem with PVA paints is that they soften up and loose their adhesion to the substrate under wet, damp or even under humid conditions, (which, incidentally, is why so many people have paint problems in bathrooms, and keep getting told that the problem was insufficient paint preparation like cleaning and sanding down the old paint and such. It wasn't, the problem was that an inexpensive PVA latex paint is not going to perform well in a humid environment like a bathroom.)
So, if you suspect it could just be a case of paint sticking to paint, then getting the joint between them wet and allowing the paint to absorb moisture is gonna soften the paint, making it easier to separate the joint.
Here, if you want to know more about latex paints in a few hours than most people working in paint stores, go here:
Continuing Education Requirements for painting tips and advice - Paint Quality Institute
and download and read the two PDF files entitled:
"The Ingredients of Paint and Their Impact on Paint Properties"
"How Color Is Affected by the Ingredients of Paint".
Post again if you have any questions about anything in these two PDF files.