Russian news sources are notoriously unreliable especially concerning terrorist hits, but FWIW:

Siberian woman alleged to be 'black widow' suicide bomber in terrorist strike in Volgograd
The Siberian Times, 29 December 2013

Oksana Aslanova, 26, born in Tyumen region, named as killer in train station massacre.

At least 16 were killed in the attack on Volgograd railway station in southern Russia just six weeks before the 2014 Winter Olympics. Law enforcement officials named Islamic 'black widow' Oksana Aslanova, 26, as being responsible for the carnage. 

While DNA tests had not confirmed this, Aslanova was widely reported as being the perpetrator. She had been on the wanted list for almost two years.

Russian news source Life News published a picture of what it reported was her bloodied head lying amid a pile of debris with her long brown hair spread across the floor. She was reported as having been married to two Islamic militant leaders liquidated by Russian forces in the North Caucasus. 

She formerly lived in the town of Raduzhniy in Nizhnevartovsk district of Khanty-Mansiysk region, with population of 43,580.  

'Aslanova was a wife of 'General' Validzhanov, who was destroyed,' said a bulletin issued last month expressing concern over her whereabouts, and predicting she could make an attack. 'She went through a training in camps and can become a black widow and take part in preparing terrorist attacks on the territory of Russia', said the Dagestan Interior Ministry.

Initial reports said she had two accomplices in Volgograd [....]

The above article mentions a photo of the severed head being published in Life News;  that can be found at the end of the Life News article in Russian here.

Local news sites reported that people in Volgograd, a city of more than 1 million inhabitants, were avoiding public transport and walking to work on foot.

"For the second day, we are dying – it's a nightmare," a woman near the scene told the Reuters news agency, her voice trembling as she choked back tears. "What are we supposed to do – just walk now?"

from

Volgograd: many dead in second explosion in Russian city
At least 14 people killed in trolleybus explosion, the day after 17 died in another suicide attack at city's railway station
By Leonid Ragozin in Moscow, theguardian.com, 30 Dec. 2013  

Volgograd blasts: Putin vows to 'annihilate terrorists'
BBC News, 31 Dec. 2013

[....]  Mr Putin said: "We bow our heads in front of the victims of the terrible acts of terror.

"We will fiercely and consistently continue the fight against terrorists until their complete annihilation."

More than 5,000 officers were deployed on Tuesday morning, regional security spokesman Andrei Pilipchuk said.

Extra reserves and the "maximum number of police and interior ministry soldiers possible" were being brought in, he said.

As many as 600 police officers from the city were recently transferred to Sochi, 688km (428 miles) to the south-west, to help with preparation for the Games which begin on 7 February, Reuters news agency reports.

Events for New Year's Eve, such as children's parties, have been cancelled in the city, while residents have been asked not to set off fireworks [....]

Note sidebar analysis on same page, by Oleg Boldyrev BBC Russian, Volgograd:

Volgograd's streets are buzzing with special buses that carry police and military patrols. Soldiers are in full battle gear with helmets and bulletproof vests.

At the entrance to a large shopping mall police asked everyone to open their bags and unbutton coats. Everyone was treated with respect and people, mostly sales assistants queuing to get inside, were very patient.

However, one could immediately see many issues here. How long will the queue be when the shopping mall opens to the public? Is not such a gathering of people in a single place a security problem?

Some residents say new security measures, however chaotic, bring some relief. Others are quite sceptical. They doubt that policemen and soldiers will be able to find a bomber in the crowd. But almost everyone I spoke to said they wished these measures had been introduced in October, after the first bomb attack on a bus.