No one wants their precious moment to be ruined and that’s exactly you’re going to do! Just remember no to go too far or it may cost you your friendship.
Think of this:
“How would you enjoy your date if your friend suddenly show up and end up ruining the moment? Simple, you just get rid of your friend! How? Set her up on a date of her own so she will no longer be bothering you on your date!”
Just make sure that you make it appear that you don’t have an idea that you’re distracting your friends’ date or else she might think that you’re just insecure that’s why you’re ruining their moment.