If the virus is constantly mutating how long would any vaccine be effective and how effective? She seems to think its not very effective at all and could be of danger to some.
The virus should mutate in a direction that optimizes species (Technically an inaccurate term !) survivability. It should optimize where it spreads easily but is nonlethal toward the host. Lethality limits spread. Ideally it should stay with the host long enough (Until antibodies natural or otherwise make that untenable!) where the host sneezes coughs to get a good virus community on its way.