A blender is not recommended for making meringue because the blades in a blender are very sharp and are spinning at too fast of a speed.
Because the blades of a blender are so sharp and spin so fast it means that the mixture of meringue gets cut through and not mixed to the right consistency.
So you could use a blender to make meringue but the consistency of the meringue won't be right and it won't be as good.
If you don't have a whisk or don't want to use a whisk then use an electric hand mixer with a whisk attachment to slowly beat the mixture of the meringue.
When you beat the eggs for the meringue you want to be as gentle as possible to get the right consistency and a blender will be too harsh on it.