Why would it be weird to ask that to begin with? As long as you ask with an ambiguous tone of voice and you don't sound too enthusiatic about it and ask her other things in the process she probably won't catch on.
I don't think you need a scenario or some complicated scheme or plot. Just use common sense and what you can use in the moment.
I think so long as you don't bring it up more than once she won't put too much attention into it or understand the significance.
If the whole point is to simply know the information but never get into a ticklish situation, then asking her once is all you'll need. And if she catches on and starts asking you questions you can take the gamble and go with it, or deny, deny, deny.
Either way, I think you win. And if she doesn't answer you then thats the risk you were taking in asking her anyway, scenario or not. Ultimately, you can fantasize about her any way you want regardless of what you know or do not or whether this pans out for you.
Since you talk with her often your chances seem good to accomplish what you want.