A former SNP MP found guilty of stealing almost £25,000 from two Scottish independence groups has lost her appeal against her conviction.

Lawyers acting for Natalie McGarry, who was elected as Glasgow East MSP in 2015, had claimed in her appeal that her embezzlement trial was prejudiced by a “tsunami” of Twitter posts saying she was already guilty ahead of the full hearing.

But on Thursday, the Court of Criminal Appeal rejected her appeal, confirming “there were strong enough safeguards in place” to give the 41-year-old a fair trial.

Lady Dorrian, who gave the judgment, compared the social media posts to “the modern day equivalent of gossip and tittle-tattle at the bus stop or the pub”.

She said the jury was given “four-and-a-half pages” of instructions to “put out of their minds anything they may have read in the past about the accused or circumstances relating to the charges”.

She added: “These were thorough and careful directions, making the position abundantly clear, and there is no basis for thinking that the jury did not follow them.”

Judges refused the appeal against conviction, but McGarry’s sentence of two years was changed to 20 months.

McGarry was found guilty of stealing £19,974 while treasurer of Women For Independence (WFI). She was also convicted of taking £4,661 while treasurer and convener of the SNP’s Glasgow Regional Association.

She was jailed for two years following the trial in June last year.

Gordon Jackson KC, who was defending McGarry, insisted she was the victim of a miscarriage of justice because of the posts about her circulating on social media ahead of the trial at the High Court in Glasgow last year.

He previously told the court there was “a tsunami of tweets just before the trial started and the jury was empanelled” which he described as “nasty, very personal, very unpleasant but most importantly, majoring on the point that this is someone who has already admitted their guilt”.

He claimed they would have influenced the jury, and that the Crown did not do enough to remove them at the time.

But in the judgment, Lady Dorrian concluded: “The question is whether these posts presented a degree of prejudice to the fairness of the trial, in respect of the independence of the tribunal, so grave that no direction of the trial judge, however careful, could reasonably be expected to remove it.

“We are satisfied that this is not such a case… there were other strong safeguards which enabled a fair trial to take place.”

McGarry, of Clarkston, East Renfrewshire, also appealed against her two-year prison sentence.

In her judgment, Lady Dorrian quoted Sheriff Tom Hughes, who at the time of the trial told McGarry: “The jury have accepted that you had lied to others, deceived colleagues you were working with and embezzled funds from organisations who entrusted you with their finances.

“In particular you had obtained money from colleagues and people who looked up to you when you falsely claimed to them that you are (sic) about to be evicted from property you had been renting.”

In response, Lady Dorrian said: “It seems that the sheriff took this into account in reaching the sentence which he selected, leading him to impose a sentence which may properly be described as excessive.”

She confirmed judges reduced the former MP’s sentence to 20 months.

A jury found McGarry guilty by majority following the six-week trial.

The court heard from dozens of witnesses, including former Scottish health secretary Jeane Freeman, who said she reported McGarry after noticing a significant shortfall in WFI accounts.

McGarry’s bank records were also presented before the trial, which showed Crowdfunder donations from WFI being transferred to her own personal account.

It included £10,472.52 on April 29, 2014 and a further £9,848.70 on November 12, 2014 – which she used to pay rent and for shopping.

McGarry had said these were “legitimate” expenses which she had incurred and which she was reimbursing herself for.

Her legal team admitted her finances were “disorganised” and “chaotic”, but she denied the charges.