Reema moved from modelling to acting soon after. Her first film was a low budget film, Chitram, in Telugu, in which she acted opposite Uday Kiran. Later she appeared in the Tamil film, Minnale, which was very successful. She tried to enter Bollywood but her first Hindi film Hum Ho Gaye Aap Ke flopped, and she decided to continue working in Tamil cinema. Her latest movie Rendu was also a successful movie in the Tamil cinema. Her facial expressions in the film Thimiru earned her the name "cute" and her horrific role in Vallavan gave her the name "extremely talented".
In April 2006, a Madurai court issued non-bailable warrants against Sen and Shilpa Shetty for "posing in an obscene manner" in photographs published by a Tamil newspaper. The report stated that the two actresses had failed to comply with earlier summonses for the same reason, hence the issuance of the warrants. The petitioner submitted that the paper had published "very sexy blow-ups and medium blow-ups" in its issues December 2005 and January 2006 issues, and which allegedly violated the Indecent Representation of Women (Prohibition) Act 1986, Young Persons (Harmful Publications) Act 1956, and the Indian Penal Code Section 292 (Sale of Obscene Books). The petitioner further demanded that the images should be confiscated under the terms of the Press and Registration of Book Act 1867.
Sen responded that she had not received any court summons and also discounted the charges. She further claimed that the pictures were freeze-frame shots from a recent movie that only exposed her navel. "As far as my photographs go, what is obscene about it? If navel-showing is obscenity, then our traditional Indian outfit - the traditional sari - should be banned in the first place."
In January 2007 outgoing Chief Justice Y.K. Sabharwal confirmed that Sen had written to him in order to enunciate guidelines against frivolous lawsuits against artists, but refused her plea on the grounds that she should have filed a formal petition instead of writing a letter.