Your mother's GP is right in recommending to take Sinemet half an hour before meals. It is best absorbed on an empty stomach (I take my first dose of the day on an empty stomach, half an hour before breakfast), but this might be uncomfortable (nausea, dyspepsia), if so take a biscuit with it. Drink plenty of water with it to send it on its way. Also take it at least one to one and a half hours after a meal. Do not eat heavy meals, especially avoid meals high in protein. Levodopa( one of the two ingredients of Sinemet) is an amino acid (as is protein) and therefore competes with the food protein for absorption. Taking it with a meal as might have happened in hospital in itself does not produce the hallucinations. It would, however interfere with the absorption . Hallucinations occur usually with high doses of levodopa (Sinemet). As absorption is delayed when food is present, the next dose could arrive before the previous one had started to work , causing this "overdose" effect. Hallucinations appear (they are usually visual and often the patient knows they are not real) more frequently to older people and with higher (too high) doses of PD drugs.
Vivid dreams, whether pleasant or not are common with PD. My dreams are usually quite pleasant, but I cry out occasionally and even fling my arms or legs about (acting out the dreams). This is quite normal for PwPs, but sometimes a husband/wife or partner does get woken up or worse, might get hit.
A considerable number of PwP , who have to go into hospital, , often on wards where they do not know anything about PD, deteriorate because their drug times are being messed about. That's why Parkinson's UK started the campaign "Get it on time". If there is a next time, keep on pointing out to the nursing staff how important the timing is for a Parkinson's patient.