Although Gillian McCusker had fallen out with Rachel and Nyomi Fee just before the two-year-old's death she had been very close friends with the pair.
She said she never suspected any wrongdoing during the time she knew the Fees.
The couple were convicted of killing Liam at his Fife home in March 2014.
They had blamed another boy for the murder.
Ms McCusker said she would now change a "friends forever" tattoo, that she had done with the Fees, so she would not have a daily reminder of the women.
She said: "I was shocked, totally shocked when everything happened.
"I looked out of my window and I saw a load of ambulances and I saw them standing in the street shouting 'help'.
"I didn't know what to do at the time as we weren't talking."
Ms McCusker said she regretted that "nothing" could be done now that Liam was gone.
Ms McCusker said that when she went into the Fee's house to feed their snakes when they were on holiday in St Andrews there was "nothing out of place" to make her suspect the pair were doing harm.
She said: "They are going to be in jail for sometime but they don't even deserve a place in prison because they are still going to get everything paid for them and they are still going to get every day of their lives.
"It's not fair because they are going to come out and they are still going to have their own lives to lead and little Liam, where is he? Nowhere.
"He's not got a life. So it's never going to be enough, never."
She said there was nothing she could have done to stop the couple as she was unaware there were any problems.
The former friend also said she did not think social services could have done any more to help the children.

The court in Novorossiysk gave two of the dancers 10 days in jail each, a third 15 days and two others received fines on charges of petty hooliganism.
Prosecutors had said their "erotic and sexual twerk dance" was disrespectful to historic memory and unacceptable.
Earlier this month, Russian officials closed a dance school after a similar dance video emerged on the internet.
The latest incident involves six dancers - one of them a minor who was not convicted - who had posted a video on YouTube.
"This incident of disrespect for the memory of war history is unacceptable  and any attempts to desecrate sites of military glory will be stopped  immediately," prosecutors said.
The sentences come as Russia prepares to mark the 70th anniversary of  the World War Two victory.
They also follow the incident early in April when a video clip from the Orenburg dance school on YouTube was viewed millions of times.
The video clip, entitled Winnie the Pooh and the Bees, showed a group of teenage girls dancing on stage in striped leotards, long socks and mini-skirts,
They perform hip-thrusting moves characteristic of twerking.
A committee is investigating whether the performance amounts to negligence or even "debauched action", which is punishable by a range of sanctions from community service to three years behind bars.

After the mansion's contents were removed and charred timbers were carefully lifted out by crane, an archaeological salvage operation got under way which will continue until the spring.
Some of the first photographs of the ornate carvings saved by archaeological experts are shown here:
A former friend of the women who murdered toddler Liam Fee has told the BBC that "no sentence" could ever be enough for their crimes.
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A Russian court has jailed three women for performing a twerking dance in front of a World War Two memorial.
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Since a devastating fire hit 18th Century Clandon Park in Surrey, reducing it to a shell, more than 400 objects have been salvaged from the burnt-out remains - but work continues on the fabric of the building itself.