older woman has needs, too

I take care of my fiancé's 81 year old grandmother who currently lives with her son and grandson with her bed in the living room next to the front door entrance. Her husband died a year and a half ago, and she's now obsessed with marrying her cousin and making love to him(she was adopted, no blood relation). He is, of course, already married to someone else, so that cannot happen. For awhile, i just thought she was lonely, which I know she is, but today she started asking me about vibrators, whether I had one, what kinds there are, how she could go about buying one, etc. my question is, I want to provide her with a vibrator, but it's awkward because she lives in the living room, and people are constantly coming in and out of the house from her care team. I can only Imagine if someone were to walk in on her...I thought about getting one of those discreet lipstick vibes, but I still don't know where she'd use it. I should mention that she is occassionally incontinent and is in the early stages of dementia. She also has peripheral vision problems on her left side. Suggestions are greatly appreciated.