Mairead McGuinness lashed out at the Prime Minister on BBC’s Newsnight, after she raised the issue of international security at Thursday night’s summit dinner.
Mrs May urged EU leaders to “consider what is in the best interests of the safety of your citizens and mine” when it comes to sharing security information after Brexit.
Ms McGuinness said she did not think the “intervention will have helped”.
She told Newsnight: “I’m quite curious as to why this issue would be thrown on the table.
“It may not be a helpful move, and on security Michel Barnier recently made quite a big speech about this.”
Ms McGuinness suggested Britain should accept losing security access as part of the deal when it comes to leaving the EU.
She continued: “Theresa May understands the value of being part of the European Union for citizen’s security.
“Obviously when the UK has voted to leave the European Union, therefore you remove yourself from all of those issues including security co-operation.”
At the Brussels dinner, Mrs May said Britain losing out on security schemes would make it harder to fight terrorism.
She said: “We would no longer be able to share real-time alerts for wanted persons, including serious criminals.
“We would be able to respond less swiftly to alerts for missing people on either side of the Channel and reunite them with their loved ones.
“Our collective ability to map terrorist networks across Europe and bring those responsible to justice would be reduced.
“That is not what I want and I do not believe it is what you want either.”
She said EU leaders should tell their negotiators to allow the UK to continue to take part in schemes like the Prum mechanism for sharing DNA profiles.
But, Ms McGuinness hit back at the allegations the EU would be putting people in danger, and said everybody was keen to provide protection.
She said: ”There is a desire on the EU side and I think the UK to make sure that we don’t endanger our citizens.
“I’m not sure tonight’s intervention will have helped us make progress at a time when we are losing hours and days to get things done.”
Security was just one issue discussed in the mammoth t10 hour long talks at yesterday’s EU summit.
Migration occupied most of the discussing time, with leaders taking six hours to come to an agreement on asylum and refugee policy.