The mum-of-two had been in the job just two months before her brother helped carry out the attack, which left eight bystanders dead and 48 injured.
A source told The Mirror the mother-of-two had her contract terminated following a probe over staff vetting procedures.
In total, eight people died and 48 were injured
She added: “You should take it up with Heathrow.”
It is believed Usman, who has worked at the airport for seven years, is still suspended.
Staff at London Bridge station embrace after observing the minute’s silence
Speaking about the suspension, a Heathrow spokesman said: “Our top priority is always the safety and security of our passengers and colleagues.
“In co-ordination with the authorities, an investigation is under way and as a precautionary measure, we have taken action to suspend two individuals.”
In the aftermath of the attack, terror expert Colonel Hamish de Bretton Gordon has demanded more background checks for security jobs at key UK sites.
He said: “Security roles at places such as Heathrow are critical — these are the people stopping terrorists putting bombs on planes. We need to be doing more to check the names of employees against terror watch lists.
“We can’t suggest this sister is in any way sympathetic to her brother’s views, but there have been enough terror cases where relatives have been acting together for the need for these checks to be done.”
Butt was shot dead by terror cops during last month’s stabbing frenzy.
Fellow killers Rachid Redouane, 30, and Youssef Zaghba, 22, were also gunned down by armed officers.