What are some signs that my MIL is bipolar/menopausal?

It's probably menopause and maybe just her personality. It really is nothing like Bipolar. People with Bipolar go through long periods of being depressed and manic (weeks to months to even years), they don't switch on and off every few minutes. Hot flashes are a definite sign of menopause. Even without the menopause she doesn't sound like a very nice person but it is not bipolar. You are just stuck with the MIL from hell........