Jessica was slammed for "textbook white privilege" when black Canadian influencer Sasha Exeter shared Instagram screenshots by Jessica that threatened her livelihood.
The stylist was then sacked from her TV credits on bridal show I Do, Redo and Good Morning America and issued an apology that referenced Meghan's own experiences concerning race.
The source added that Jessica is “losing so much work from brands who loved her connection to Meghan in the past but now feels she has become toxic."
“All it would take is for Meghan to go out on a shopping trip with Jessica to show she still has her support. But the clear indication is that there’s not going to be any show of support like that.
“It’s a brutal blow after a ten-year friendship. Jessica has been there for Meghan through thick and thin.”
Jessica and Meghan became friends when the latter moved to Toronto to film her television series Suits.
Their bond grew over the years - Meghan is the godmother to Jessica's nine-year-old twin sons Brian and John and all three Mulroney children were in Harry and Meghan's royal wedding bridal party.
The Canadian mum shared a photo of her sons carrying Meghan's veil to Instagram with the caption "Proud friend. Proud mum."
Meghan and husband Harry haven't addressed the rumoured Mulroney feud but are instead focusing their efforts on the Black Lives Matter movement.
The couple recently participated in a video chat with a selection of young leaders and activists and addressed how it's important to acknowledge "discomfort" in conversations about race.
"We're going to have to be a little uncomfortable right now, because it's only in pushing through that discomfort that we get to the other side of this and find the place where a high tide raises all ships," the Duchess of Sussex said on the call.
"Equality does not put anyone on the back foot, it puts us all on the same footing - which is a fundamental human right," she said.