Boon had been on a long weekend hen do in Milan with five others before her airport ordeal.
The 59-year-old, from Staffordshire, says she has paid for an apartment in the city as she waits to take a flight to Gatwick on Tuesday.
Her group was among at least 100 people left waiting in a situation she described as “very stressful; people arguing, someone fainted, someone was sick”.
A spokesperson for EasyJet said it had warned passengers to allow extra time to travel before the “longer than usual waiting times at passport control”.
But Boon said: “Even if we were there five hours before, we weren’t told the gate number until about 90 mins before, so there was nothing we could have done.”
When they were told their flight had left, she said EasyJet representatives then “left us to fend for ourselves”.
She added: “It was just disgusting the way they spoke to us.”
Hume, 56, from Leeds, said the waiting had been “awful, just a mess”.
He said he had spent more than £1,800 arranging to travel via Luxembourg so he could return to the UK as soon as possible.
“EasyJet offered us £19 and a flight on Thursday,” said Hume, “but we would have had to pay £300.”
The airline spokesperson said the flight had been held to allow customers extra time, and it had provided “free flight transfers to those affected”.
EasyJet apologised but said the problems were “outside of our control”.
“We continue to urge border authorities to ensure they make full and effective use of the permitted flexibilities for as long as needed while EES is implemented, to avoid these unacceptable border delays for our customers.”