Lawyer Lee Suet Fern's "singular focus" in achieving what her husband Lee Hsien Yang wanted, oblivious to the interests of her father-in-law Lee Kuan Yew, was a factor that weighed in favour of a heavier sentence.

Not having due regard for Mr Lee Kuan Yew's interests was a "grave failure" on Mrs Lee's part, a Court of Three Judges said in its judgment yesterday as it set out the various factors that it considered in deciding to suspend her from practising law for 15 months after finding her guilty of misconduct over her handling of the late Mr Lee's last will.

The preparation of a will is not just a routine exercise in form filling, said the court.

A lawyer who is tasked to prepare and attend to a will has serious responsibilities and should conscientiously avoid being in any situation where even a potential conflict of interest may appear to exist, said the court.

"A solicitor who fails to act with exceptional care and... with restraint and circumspection must be prepared to have her conduct scrutinised and, perhaps, even her motives called into question," said the judgment written by Chief Justice Sundaresh Menon.

While the court accepted that there was no solicitor-client relationship between Mrs Lee and her father-in-law, it said the current case was analogous to cases involving lawyers who prefer their own interests over those of their clients.

Given the absence of a solicitor-client relationship, the presumptive penalty of striking off would be disproportionate, said the court.

"Nonetheless, the sanction that is imposed on (Mrs Lee) should reflect both her culpability and the harm caused by her misconduct," said the court.

On the afternoon of Dec 16, 2013, Mrs Lee's husband Lee Hsien Yang, who was going overseas that evening, told her to make arrangements for the senior Mr Lee to revert to his original 2011 will.

The court said that upon being told this, Mrs Lee was well aware that she was in a position of potential conflict as her husband had been a significant beneficiary under that will.

Despite this, she set about locating a draft of that will and sent it to the senior Mr Lee, telling him that it was the first will he had executed in August 2011.

The court said Mrs Lee was so focused on what her husband wanted done that she did not check with Mr Lee Kuan Yew to ensure that he indeed wished to revert to that will.

She also sent the draft will to her father-in-law without even checking whether it was the final draft of the first will.

After the last will was executed, Mrs Lee asked her husband, rather than her father-in-law, what she should do with the two original copies of it.

The court said her "remarkable lack of diligence" in ensuring that her father-in-law's wishes were properly ascertained and that he was fully apprised of all the facts also weighed in favour of a heavier sentence.

Mrs Lee's experience of more than 30 years also weighed against her.

"While this was the first blemish in the course of a long career, her significant experience rendered her conduct wholly unacceptable and inexcusable," said the court.

On the other hand, the court found that the lack of dishonesty in her dealings with Mr Lee Kuan Yew was a factor in Mrs Lee's favour.

While the court said Mrs Lee was "clearly imprudent" and "grossly negligent", it noted that she had testified that she would not have dared send out the draft will if she did not think that was what her father-in-law wanted.

However, the weight to be placed on this factor is lessened by the fact that she acted with a degree of dishonesty in the disciplinary proceedings by giving a "contrived and ultimately untrue account" of her role in the preparation and execution of the will.

Considering all these factors, Mrs Lee's culpability was at least "moderately high", the court said.

It added that material harm was caused because Mr Lee Kuan Yew ended up signing a document which was in fact not the one that he had indicated he wished to sign.

"The fact that the last will and the first will were materially similar was fortuitous and does not discount the fact that the potential harm could have been far more severe than the actual harm that eventuated," said the court.

It noted that while Mr Lee Kuan Yew had changed his will several times, he was content with the last will after it was signed and lived with it for more than a year and did not revisit it, apart from bequeathing two carpets to Mr Lee Hsien Yang.

The harm caused in this case was "at the lower end of the moderate range", it said, adding that a substantial period of suspension was warranted in this case.

Before determining the appropriate period of suspension to impose, the court looked at three precedents in which the errant lawyers involved were suspended for between two and three years in cases involving a conflict of interest.

Comparing the facts of the current case with the precedents, the court said a 15-month suspension was appropriate.