Is a girl's refusal to marry a suitor because of his job instability, or her mother's desire for her not to emigrate, or due to an age gap, considered disobedience to Allah despite the clear hadith on the matter?

Accepting a suitor for marriage is not obligatory, unless the woman is in need of marriage and fears hardship for herself by remaining unmarried. In such a case, her guardian must marry her off, and it is forbidden for him to prevent her from marrying. There is no harm in rejecting the suitor if you wish to obey your mother and do not fear temptation for yourself; Allah will compensate you with someone better.