You can go Ana and do mind games with her DM. Don’t use sleep unless shes not looking or if she is low on DM or if you are 1 HP. Save your nade for a last resort to heal yourself and run away. Don’t try to kill the D.Va unless you are sure your team is ready to help you.
Most Anas in my rank will panic and use their sleep too early if you dive them so if you don’t they will probably think you don’t have it and drop DM. Don’t just stand there though you have to look scared or they won’t fall for it. If you do this a few times the D.Va will get annoyed and either respect you more and leave you alone or take it personally and hard focus you even more.
If its the latter then just play farther back and make her go way out of position to dive you like those annoying GM’s always do. If they start sending a Tracer or something else after you then yeah prolly time to switch unless you’re one of those crazy unkillable Anas.