I believe she can, and that is technically an option. The problem is that this could destabilize the country. Citizens voted and asked for a Brexit to happen. The government is trying to honor that request as it is a democratic country. If it just decided to ignore the vote and cancel any plans for Brexit, the British government would do irreparable harm to the idea of democracy in Britain.
In Switzerland it is not a problem to repeat a vote, either after about ten years or if there are new circumstances justifying a re-evaluation or if the proposition has been modified to appease the opponents. Some proposals needed several retries to be accepted by the Swiss. It takes time.
I seriously think that UK should stop the process and start again. This is not undemocratic because people now know better (new circumstances justifying a re-evaluation). The process would be like this:
1. The parliament decides to cancel the process
2. A Spanish judge made a proposal how to halt the Brexit
3. An emergency committee tries to find a temporary deal with the EU
4. After a year or so, the popular vote is repeated
The leave voters will just complain, but it avoids all the chaos and cost associated with leaving, when there's no clear benefits.