I hope she doesn't find out before you're ready to come clean for yourself.
And, more importantly, I hope you
do eventually come clean for yourself.
I mean, if you require a suggestion on something clever to assuage the potential 'anti-gay rage', then just come out as a liberal first. Then, after she recovers, you can tell her you were just kidding, and that you're really conservative, only homosexual.
Sure you'll still be lying to her for the time being, but once she gets used to the concept that you're homosexual, then you can come out as actually being a liberal, too. I think that'll weigh more heavily on her than anything.
“…Judge not what a man has done, but judge what he could have done if he was a different bloke altogether. For art thou a leper? And a leper can changeth his spots…” --Rudy Wade, Misfits (Series 4, Episode 8)