Estrace, or estradiol, is an estrogen that was circulating in your bloodstream, produced by your ovaries, for 40 years or so! Any allergy is likely to be to the "vehicle," the substance that contains the estradiol as an active ingredient. I assume your reaction was local--in the area where you applied the cream.
An option that may work for you is Vagifem, a bioidentical estradiol in tablet form that you place in the vagina twice a week (usually after starting with daily use for 14 days). Vagifem comes with a very slim applicator to place it in the vagina.
Another choice might be Estring, another bioidentical estradiol in the form of a ring. The ring is placed in the vagina for 90 days and is then replaced.
Take the time to find an option that will work for you!