Not a lady but I have to ask, what would you be hoping to achieve by getting her a dildo and what sort of message do you think that sends? If you know she's into toys and you want something you can both play with that's cool. Or if she collects dildos and this is a size she doesn't have, again that would make some sense. But to out of the blue get her a dildo that's bigger than your cock, and you don't know what she likes? I don't see how that's going to go over well. Also it sounds like you're doing it out of insecurity, which most women find unattractive.