That's a big prediction against Emma, does Pam saying that she is just a one hit wonder? (well this was the case in women's side though, there are some who after winning a grand slam suddenly drops out of the top 10 and was never the top player they are).
But we can see that after the changes coach, her game has deteriorated. But we will have to see, hopefully she can still compose herself and still be like the player that suddenly break into the limelight last year specially winning the US Open.
That are strong words from Pam Shriver but as you say, we will need to wait and see how Raducanu continues to develop this year. She struggled in the tournaments after her US Open as there was a lot more pressure on her (before she was always in the underdog position). Changing her coach was maybe not the best idea, but only time will tell.
Maybe it was just me, or Pam is a hater of Emma because of her recent success but then again, she is trying to shoot here down with that negative comments of her against the teenager? Or she is just trying to keep the fire burning inside of Emma to really go and strive for more in 2022?
In any case the ball is on Emma here, to prove her critics and detractors by winning another grand slam or at least a tournament and break into the top 10 this year, that will be her goal.
I don't think Pam Shriver is being objective, there's something else going on, maybe she just dislikes Raducanu, or resents her early success? Or - more likely - she is thinking of her own career, where she reached the US Open final as a 16 year old, and then never ever reached another slam final again (see image below).
To be ranked in the top 20, you need to accrue around 2500 points over the calendar year. Given that Raducanu will be seeded in a lot of tournaments due to her current ranking, this doesn't seem a huge ask. The US Open wasn't a one-off, you don't win these things just by being lucky. Remember this was actually her second ever slam, in her first one, Wimbledon last year, she got through to the last 16 as well, and could quite easily have made the quarters if it wasn't for her medical issue.
https://en.wikipedia.org/wiki/Pam_Shriver#Career