You cannot sack her for being pregnant, but in theory at least the fact that she is pregnant should not stop you from sacking her for one of the five fair reasons (see question 2). But be very careful. You need to be very certain that her behaviour cannot be attributed to the pregnancy (which might be a cause, for example, of poor timekeeping - because of morning sickness - or absenteeism), and you need convincing evidence of the behaviour for which you are considering dismissing her. Take advice.
