I think the mooncup, as mentioned before, sounds like theideal solution. I've never used one butI know people do really like them. I don't know whether they're more difficult to use if you're a virgin though [that's a complete assumption, but given your background?] but you can have the same issues with tampons so...
With mooncups there is no evidence basically. You just wash the blood out and reinsert. When you're not on you could just hide it - it'snot very big. She'd never have to know - unless she would notice the lack of used sanitarty towels etc?