Is her rejection of my proposal, under the pretext of discomfort, after performing Istikhara and consulting her family, an indication that this marriage is evil, despite my feeling that she still desires it, or should I try again?

Since you sought Allah's guidance through Istikhara and took the necessary measures, and the matter did not materialize, there is no blame upon you. Perhaps Allah averted an evil from you. The woman may have a reason for her concealment. Look for someone else, and if she agrees later, there is no harm in completing the procedures. This does not contradict the outcome of the Istikhara.