and the old review will be taken down when the new one goes up.

You must have seen the gal within the 90 day window in order to write the review.

Editing can only be done in the day or two between submitting a review and its being published.

Mrfisher is talking about writing a new review, which you can also do if it is a recent visit.
But you can also edit a review, by contacting admin and telling them why you need to edit it. (For example you gave out too much info on the lady, or something in the review was blatantly wrong). It has to be a good reason but if admin agrees, they will put your review back in edit mode for you. You can edit and resubmit it. I know this from personal experience.

If you just submitted it, and it hasn't been approved yet, (under myreviews it will say "new" and there will be an edit button.) then you can edit and re edit until they approve it. Once it is approved, you have to use the "contact us" button.