Is it permissible for an engaged girl to refuse marriage to a wealthy suitor who proposed to her, and to hold onto her first fiancé who is not wealthy and is still in military service, and would that be considered disobedience to her parents?

If an agreement has been reached with the first suitor, it is not permissible for another to propose to you. An engagement cannot be broken except for a legitimate Shar'i (Islamic legal) excuse. Piety and good character are the criteria for choosing a suitor. A prolonged engagement may be a valid excuse for its dissolution, especially if there is fear of harm. What is considered in accepting a proposal is the statement of a mature woman if she is not coerced, and the statement of the guardian if she is coerced. The preponderant opinion is that a mature, sane woman cannot be forced into marriage.