As written, one Element must be chosen for each use of this ability, applied to a selection of allies.
The entire line for use of the Elemental Glyph class feature, with emphasis added:
As a move action, the mystic can spend one point of animus to apply an elemental glyph to a number of allies equal to her mystic initiation modifier modifier within her sight.
This is different than choosing a number of allies to supply Elemental Glyphs to. Without specifying that you can change the glyphs selected for each target, you default to doing exactly what the text says.
It is unclear if this was intended to be the function, and you should speak with your GM if you feel it's more thematic or balanced to ignore. However, this is in-line with standard Pathfinder abilities, such as Communal spells and Bardic Performance.