A man approached her from behind and shoved her to the ground at about 13:30 GMT in Hanwell Cemetery, west London.
The suspect made off with her bag which was later recovered by a member of the public, but the purse had been taken.
The victim suffered minor injuries in the incident but did not require hospital treatment.
Police have released a CCTV image of the suspect, who is described as skinny, about 5ft 9in tall, wearing a black scarf covering his face, a grey hooded top, a black coat and jeans.
A Met Police spokesman said: "The robbery took place in broad daylight and police are keen to speak to members of the public who saw a man matching this description, walking briskly away from the scene, with his face covered and hood up."

Esther Kidemba died after apparently jumping from a building during a drill at the private Strathmore University in the capital, Nairobi.
Gunshots were fired during the drill, causing panic on the campus.
Militant Islamist group al-Shabab killed some 150 people in an attack on Garissa University College in April.
Strathmore University Vice-Chancellor John Odhiambo said he offered his deepest condolences to the family of Ms Kidemba, who was a staff member, and an "unreserved apology to every student, parent, family, colleague and stakeholder for the unfortunate outcome of the security drill".
Strathmore would pay for the medical expenses of 30 students and staff injured during the drill, and would arrange post-traumatic counselling, he added.
The drill had been carried out by the university's security team in co-ordination with local police to assess how they would deal with any attack, a statement by the university said.
On Monday, Nairobi police chief Japheth Koome said all the proper procedures had been followed for the mock security exercise, Reuters news agency reports.
But in his reaction, police chief Joseph Boinett said: "This must not happen again."
Kenya's security forces were on high alert to deal with threats, and drills should be conducted only with the authorisation of the "highest security office in the country", he added.
April's day-long assault on Garissa University College in north-eastern Kenya was the deadliest by al-Shabab in the East African state.
In 2013, at least 67 people were killed in an attack by the al-Qaeda-linked group, which is headquartered in neighbouring Somalia, on the upmarket Westgate shopping centre in Nairobi.
Al-Shabab says it is opposed to the presence of Kenyan troops in Somalia.
The troops are part of an African Union (AU) force helping the weak Somali government fight the militants who want to establish Islamic rule in the country.

A total of 177 roads have been lined up to be reconstructed this financial year, Surrey County Council said.
The remaining roads in the Â£100m project will be dealt with over the following two financial years.
Each of the roads will have "better, longer-lasting surfaces" and will be guaranteed to last 10 years.
Work planned for this year includes the Godstone and Farnham bypasses, the Scilly Isles roundabout in Esher, West Street in Dorking, and Staines Road West in  Sunbury Common.
A 73-year-old woman had her handbag snatched as she was cleaning her husband's grave on Christmas Eve, Met Police have said.
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Kenya's police chief has warned universities not to carry out security drills without his approval following the death of a woman on Monday.
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More than 800 roads in Surrey are to be given "pothole proof" coatings over the next three years in an initiative to overhaul more than 300 miles of road.