Rajnaara is a socio-legal researcher with a focus on family law. In particular, her research centres on marriage formalities and legal treatment of non-legally binding religious-only marriages. Her research into such marriages looks at transitional relationship norms, normative influences, legal consequences and autonomy. She has conducted extensive empirical research on family law and family justice processes in the UK, Qatar and Australia. Her work draws on a range of socio-legal theories and approaches, and is underpinned by Critical Legal Theory.

Rajnaara has undertaken several grant funded projects including recently completed collaborative research funded by the Nuffield Foundation for which she was the Primary Investigator, exploring why marriage ceremonies occur outside of the legal framework for weddings in England and Wales. A second project where she is Primary Investigator, funded by the Doha International Family Institute, explores the experiences of women in Qatar engaging with the law and legal infrastructure relating to marriage and divorce.

Rajnaara has collaborated on international interdisciplinary and multi-disciplinary projects. Her research has been published in a range of law, sociology and theology journals, and she has presented her research at multiple academic, practitioner, government, and stakeholder meetings and conferences.

Other areas of interest include children's rights in family law, international child law, gender and human rights law.