Picking bridesmaids dilemma

So I planned to have 5 bridesmaids initially but now thinking of having 4. My bridesmaids are made up of my sister as moh, then a couple girls for another friendship group and another girl from a group of 3 of us. The other girl in that group of three is the one I’m considering dropping she’s just been irritating me so much the past few months I would rather not have her. When I asked the other girl to be a bridesmaid in our group and said I was thinking of not having our other friend I could tell she thought it was going to be so awkward which it will be. Our friend doesn’t know we meet up more often as we are happy to go on dog walks, go for coffee and just general catch up more regularly. She would rather it be every few months instead. The one I’ve asked to be bridesmaids said I would need to meet up with the other girl to explain the sitch but I don’t know what to say. Do I just blame it on costs or something?! Or just suck it up and have her to even though I would rather not?