As the less conventionally attractive woman, there's a few different things that could happen.
Option A: you can't, she knows she's not as pretty and has always known she's not as pretty and will feel bad about being the one who doesn't get hit on no matter what.
Option B: her and her friend are there to have fun on a girls night out and not to be hit on so she's actually happy that she's not the one being bothered. (Assuming this is In a social situation like a bar or a concert where going up to a woman and speaking to them because you are interested is socially acceptable)
Option C: The "less attractive" friend is presenting that way intentionally and is there for scary dog privilege and will back you down and make you go away because neither of them is interested in being bothered. (More likely in scenarios where it was socially unacceptable to go speak to the pretty girl in the first place, but not uncommon in social settings if the pretty girl is tired of being hit on and asks their friend to play bouncer)
Part of the reason I don't go out as much anymore is because I got asked to play scary dog privilege more often than not and it just kind of doesn't feel good knowing that you're only there to be a repellent to men.
-The humble perspective of the 5'10" but will still wear 5-in heals, 250 lb muscular woman who knows what way to twist a head to sever the vertebral artery. 🫠
Yeah that stuff is kinda why I won't bother with girls unless they show interest first. Also besides the point, I'm celibate. I'm never gonna have kids and I don't gamble. I'll still flirt though.