Some priests will follow the rules to the letter, however, and not allow even this. The same is true for music, which in principle should all be sacred. If the parish has an organist available, you may request their services. If you have friends who play other instruments they may be allowed to play, on condition that the choice of music respects the sacred character of the occasion and place. There are no restrictions on who may be present.
Most parishes help non-churchgoers to follow what is happening by providing a booklet.
Alternatively, it may be a good idea to produce a service sheet yourselves, once you have chosen the texts and hymns. Consult the priest on what should be included. It is often a good idea to give complete texts, for instance for the readings, and for prayers such as the Our Father, where everyone will be invited to join in. Other items in the service can simply be mentioned in the order in which they occur, to help your guest follow the service. Indications on when to stand, sit or kneel are always useful.