If the risk remains after your usual controls, alter her working conditions or hours of work, where that is reasonable and would avoid the risk. If it would not, offer her suitable alternative work, on terms and conditions not substantially less favourable than her own. Only if there is none can you suspend her, and she is then entitled to be paid her normal remuneration while suspended.
If she works at night and a doctor or registered midwife certifies that she should not, the same rule applies: offer suitable alternative work, and suspend her on full pay only if there is none.
Provide somewhere suitable for her to rest.