Tgirl 3some with my girlfriend

[Gladiator]

I've been thinking about asking my girlfriend if she would into a threesome with a tgirl. I'm kind of scared to ask her because I don't want to have any problems.
It would be fun but maybe she will think I am gay. Maybe she will want to break up. Maybe she will be into it. How can I know before asking?
Maybe I could accidently show her some shemale porn or something to soften her up and gauge her reacton.
Not sure the best way to approach this, I really like her but it would be fun to do it with her.