The crash occurred three weeks after Tsvangirai was sworn in as head of a national unity government following a disputed elections between the MDC and President Robert Mugabe's Zanu-PF party.
But senior officials in the MDC have not said that they suspect foul play to be a cause of the crash, she said.
"We cannot talk of foul play ... until it has been proved what has really transpired," said Tendai Biti, secretary general for the MDC and the country's finance minister.
Biti called for a police investigation into the crash during a news conference at MDC headquarters on Saturday and said the party will conduct its own investigation.
"If there had been a police escort, what happened would not have happened," Biti said. "The authorities could have avoided this omission."
Truck hit car
Tsvangirai had been travelling to a rally south of Harare, the capital, when his car was hit by a lorry travelling in the opposite direction, an MDC minister told the AFP news agency.
MDC officials comforted one another after an official confirmation of the crash [AFP]
"He was hit by a haulage truck. The driver of the truck appeared to be sleeping. [Tsvangirai] was travelling to his rural home in Buhera where he was due to hold a rally Saturday," the minister said.
Susan Tsvangirai was killed instantly while her husband suffered some head and neck injuries, state television said.
Mutasa, Al Jazeera's correspondent, said that Tsvangirai's car was travelling as part of a convoy at the time of the crash.
"People are wondering how this could happen if he were travelling in a convoy. Why was his car the only one apparently damaged?" she said.
"The coalition government is very fragile and people will speculate and start reading into it; they know the relationship between Tsvangirai and Mugabe was never that good to begin with."
"MDC officials are being very careful and don't want to cause any unnecessary tension in Zimbabwe," Mutasa said.
"They do not want to make the [three-week-old] fragile coalition government any weaker than it already is."
While Tsvangirai's wife was not actively involved in the MDC, she has accompanied her husband at the party's campaign rallies over the past 10 years.
They had been married for 31 years and have six children.
Tsvangirai was sworn in as prime minister of a national unity government in February after months of political wrangling between Zanu-PF and the MDC over a disputed presidential election, which the MDC claims Tsvangirai won.
The new adminstration is tasked with tackling severe food and fuel shortages, record hyperinflation and a cholera outbreak that the World Health Organisation (WHO) says has killed at least 4,000 people.
Mugabe, a long-time rival of Tsvangirai, visited him in hospital with his wife on Friday but did not speak to reporters.