I think, regardless of where she intends to end up, she always had to start from the perspective of the UK being completely out of the EU. Showing that the UK is prepared to stand on its own two feet. If not prepared to do so, negotiations would be very one sided. It'll certainly be interesting to see how the negotiations play out.
When Switzerland was faced with a similar issue (after citizens voted to restrict EU immigration) it was clear their Government knew straightaway they needed the deals with the EU, so it was impossible to negotiate anything of value.
Britain is politically and economically very important to continental Europe, so May does have some bargaining chips.