  The third observing run of the LIGO-Virgo collaboration has resulted in about
hundred gravitational-wave triggers including the binary neutron star merger
GW190425. However, none of these events have been accompanied with an
electromagnetic transient found during extensive follow-up searches. In this
article, we perform new numerical-relativity simulations of binary neutron star
and black hole - neutron star systems that have a chirp mass consistent with
GW190425. Assuming that the GW190425's sky location was covered with sufficient
accuracy during the electromagnetic follow-up searches, we investigate whether
the non-detection of the kilonova is compatible with the source parameters
estimated through the gravitational-wave analysis and how one can use this
information to place constraints on the properties of the system. Our
simulations suggest that GW190425 is incompatible with an unequal mass binary
neutron star merger with a mass ratio $q<0.8$ when considering stiff or
moderately stiff equations of state if the binary was face-on and covered by
the observation. Our analysis shows that a detailed observational result for
kilonovae will be useful to constrain the mass ratio of binary neutron stars in
future events.
