I can't speak for all the INTJ women (maybe this just applies to people in general?), but honestly, say it how you want, but maybe preface it with 'You don't have to respond right now and we can talk about this later... but...'
After you've had your say, if she seems like she doesn't have a ready response, let her off the hook for a bit so she can think about what you said. She'll think about it, trust me. Depending on how patient you are, you could give her a specific time when you two can meet up and discuss, or you can tell her to get back to you when she is ready. (The second one would make me more nervous than the first.)
She may not take you up on your offer to wait... in which case she'll dive right in to her response. If she does that, she's probably already thought about this possibility (to a great extent) and knows her answer. If she does this, take her at her word. My guess is if she's true to form, she won't give a solid answer unless she's thought it through. If she's blindsided by it and hasn't considered the possibility before, she'll need time to process.
Just my two-cents