yeah, where too, has she suggested any place in particular?
See this is interesting because it's out of the blue and totally unexpected.
I don't know what the email said but if applicable just tell her this: "...why don't you give me a few places you might like to have dinner at and I'll get back to you and let you know what I like from your choices."
Here's the deal behind this, you put it in her court to follow through on that date offer, you don't put any effort in that portion of it, you lead by telling her indirectly that you're receptive to the offer and you are the one making the choice to accept - take that into account. She will come up with a list of places to go to and you will select what YOU like from that list, if nothing on that list is what you like, don't just take what's offered, come up with some choices yourself.
Don't be over eager about any of this but I would go, enjoy it for what it is, an evening out, for some dinner and possibly some more conversation and heck she may have some crazy news to spring on you too so don't get your hopes up.
Another thing, if she pulls the bipolar act and goes batshitcrazy between now & then, no worries, you're expecting anything & everything and you'll be able to respond accordingly.
I'm interested in this, let me know what happens. When is the time frame for all of this?