your concern is very much valid. Though there is very little chance that she could get pregnant, it is better to be safe then sorry. Hypothyroidism may not be a problem for the pill, but one must be sure there isn't any pre existing medical condition where pill is contraindicated. Best would be to see a gynaecologist, get examined and get proper prescription for the correct medication. Next time be sure to use a condom to avoid this situation. Stay safe.