Do you have room to extend the shower toward the door?
If you do, take out the tub, move the vanity closer to the window, place the toilet where the vanity is now if that will give you more room for the shower to extend this way.
If you do extend it to the window, you could also frost the bottom part of the window, but I don't think you'll ever end up using that section of the shower other than getting in and out.

Windows in showers are where the rot enters the house. Bad idea unless you replace the window and have a contractor that understands correct waterproofing. You just described a 12-16K shower. Not bathroom. Just the shower.

I would avoid it if possible if not you need to have the right window installed for this application.

change the window to an awning style one, the same width but just in the top part of the opening. you'll need to fill on the outside so if its in the front and your house is brick that could be complicated, otherwise not. we love ours very much and as we have no abutters behind us we don't need to even have the window be frosted.