"Open-minded" means she wants you to think she'll take it in the ass, make an appointment, come see her, find out she's really a prude, start thinking with your little head and pay her for a CBJ because you're dumb and gullible.
"Extremely open-minded" means she hopes you're really dumb and will believe there's some mysterious "other" thing she does that will blow your mind. In all likelihood, it's just a copy of the Kama Sutra from 1978 and some lube.