Play fighting getting out of hand?

Hello!
My 2 sister-kitties are 2 years old. They have always play-fought, but over the past few months I am concerned that their "fighting" may be getting more aggressive. The girls are from the same litter. One is smaller than the other (the larger girl has about 2-4 lbs to lose, and is a bit of a drama-queen). The scene plays out like this:
The smaller one will chase and engage the larger one in play the way that they always have. They never break the skin or cause blood-shed. However, the larger girl will growl, hiss, and "scream" when the small one "attacks." The little one never makes a sound. Also, the big one will run to a place that she can't get out of (in a corner, behind furniture, etc) and/or takes a "defensive pose" (laying down). Then, she'll growl, hiss, and scream and if the small one doesn't go away, she'll eventually run away and the small one will chase. This will go one for a few minutes until the small one walks away.
I have no idea what's caused this change. Nothing has changed in their lives. They are always indoors. I don't think the small one is playing too rough. They still sleep together, they have plenty of toys, get lots of attention, and neither one is keeping the other from their food/litterboxes.

Am I just over-reacting to this? Is it possible that my big girl is just a drama queen? Any tips will be greatly appreciated.
Thanks!

It might be normal, but it could also mean the bigger one is sick - cats are notorious for sensing sickness on other kitties, and becoming aggressive towards the. I would take the bigger one to the vet to rule out any problems just in case.
Vibes for your girls

Thanks for the reply!
I took her to the vet last week because she was relieving her anal gland at inopportune times. The vet checked her over then and said everything seemed okay. We changed them to a higher fiber food.

I also asked the vet about this problem last week and she said it's probably normal. She mentioned I could buy some kind of pheromone emitter that calms them down, but she said that wouldn't be necessary unless one was keeping them from the food/litter.

Anyway, I trust my vet, and my cats are both very content and easy-going cats. So, the hissing, growling, and screaming is so jolting I wanted to see if there was any further information I could get.

Thanks again!

Do they get along otherwise? Like... do they hang out together, take naps together, groom each other? Or all of the sudden they can't stand each other?