Putting Alison Hammond + Mumsnet into google brings up numerous threads about how awful she is and that she's shit at her job. Hardly a good example.
The disparity between Meghan and someone like Jessica Ennis Hill is an excellent example of "stay in your lane" racism.
A black or biracial woman excelling in a field that is traditionally associated with working class people and/or people of colour simply does not trigger racists as much as the sight of a black woman "invading" a posh white space. There's a real ignorance of racial coding, history, and stereotypes at play here.
A black woman who's able to run extremely fast does not challenge racist perceptions and racial stereotypes in the way a black woman excelling in an intellectual arena does, or a black woman dominating upper class society.
There are plenty of other black or biracial public figures who draw a disproportionate amount of bile, and what they all have in common is that they occupy spaces that historically have been white and usually either middle class or upper class.
Just look at acting. When black actors play maids or slaves, there are few complaints because those roles reinforce racist stereotypes. When black actors play heroes or historical figures or even just roles that traditionally were played by white actors, it triggers racists (eg the outpouring of racial abuse over Moses Ingram being cast in Star Wars, and John Boyega and Kelly Marie Tran before her; the RSC being attacked for casting black actors in a Shakespeare play; and the recent West End production of Grease that had to issue a press statement complaining about racism because the production and cast had received racial abuse and goady articles in the tabloids just because some of the supporting characters were played by black actors).