what prescription drugs can cause sexually arousing dreams in a 74 year old woman

Careful, you may get complaints from doctors about the queue's forming!

It's actually a very interesting question. I'm afraid I don't know enough about how the pharmacology of drugs might relate to dream content (if at all) but I'll share what little I understand and maybe other people can add or improve on this.

I suppose the first thing to do is to confirm that different types of drug are known to affect dreaming. If you are taking sedatives or hypnotics, for example, the amount your dream actually reduces. Antidepressants tend to reduce a type of sleep known as REM sleep. When people come off these drugs there are reports of increased dream activities and sometimes nightmares.

I suspect that dream content is much more likely to be something of the psyche. It could well be that certain drugs provide a mechanism to bring certain memories or fantasies forward and this is what you are experiencing.