She had to work for several years to convince women religious from Africa to talk to her about experiences of abuse by priests, she reported at a press conference in Aachen on Friday.
Her dissertation "Sexual Abuse of Women Religious in Africa" was recently published in German.
"Abuse is a reality," said Lembo. Women religious are in close contact with priests, trust them and seek advice and help. This could lead to "asymmetrical relationships".
Some priests complimented the women, said the expert, while others isolated them.
There is also a certain naivety.
Women in religious orders sometimes have the idea that a priest cannot hurt them.
Social taboo
Sexuality is still a social taboo, says Lembo, explaining why abuse in the church has hardly been addressed to date.
Fellow nuns also showed little understanding.
In addition, the women were afraid and did not want to damage the image of the church.
It took her several years of work before enough nuns agreed to talk to her.
In the end, she conducted interviews with nine affected women from five sub-Saharan African countries for her study.
For her own protection, she did not name the countries in which she worked.
To better protect women religious in future, Lembo is calling for training programmes and preventative measures.
The Catholic aid organisation missio, based in Aachen, is organising projects in African and Asian countries.
At the book launch, missio President Dirk Bingener said that abuse is systemic, not an isolated incident.