@Alex1477 You say the guest likes your place and you like her. Do you have much interaction with her or do you just see each other in passing and she sticks pretty much to herself? As a home-share host myself, I have a fair amount of interaction with most of my guests- we'll chat over coffee or a bottle of wine in the evening and end up talking about all manner of things. So I can usually find a chance to mention reviews, if I feel it's necessary, without it seeming like a pointed topic. (I know there are hosts who feels it's a no-no to even mention reviews to guests, but I've done it often and never had a bad result) If you do hang out with her a bit, I'd just bring it up casually in the course of conversation. I explain that Airbnb doesn't apply the star ratings to hosts the way they explain them to guests- that you know that Airbnb tells guests that 4*s is a good rating, but that if you get too many 4*s, Airbnb sends hosts warning messages about pulling up your socks, that they unreasonably expect hosts to be 5*s all the way. In my experience, guests know nothing about this, and just believe what Airbnb tells them- that 4*s is good. I'm sure your guest has no intention of tanking your ratings if she keeps booking with you. She just doesn't realize that it can hurt you.
Simply explaining to guests the disconnect between what Airbnb leads guests to think is a good rating and how they actually apply the ratings to hosts, if you can find a way to mention it in a casual way, isn't the same, psychologically, as prodding guests to give you a 5* review, which could be seen as pushy and totally backfire. I always present it as an Airbnb faulty review system, say I think star rating systems are a bad idea in general (which I do) because what might seem like a good location to one person might not be to another, so how do you know why it got a 3* for location?, not as the guest being in the wrong or me thinking my place is so great it should always get 5* ratings.