[swhalen]

I think it's probably fair to say most cosmologists would consider her views marginal, but she is certainly not a crank. My (limited) understanding is that ΛCDM fits cosmological observations extremely well; however, neither dark matter nor dark energy has actually been shown unambiguously to exist. 'Mainstream' cosmology invariably also includes inflation, which remains essentially a speculative idea unsupported by any hard observational evidence. Sabine Hossenfelder has become a popular commentator by drawing attention to discussions of these and other issues.