sakura-san~~
truthfully, I have no idea either...
but sprain ankle + more pressure on it = something like swelling and pain?
whenever I go to a doctor for that type of thing, it isn't much of a hospital type thing
more like a clinic, the doctor will more or less say the common symptoms and not say the complicated things
basically, I guess swelling and like not being able to walk, healing will be further hindered, it is advised that you(Girl A) tell Girl B to rest a bit...
(btw, turns out that some people have to get surgery cuz of sprains, but you might not want to make it more confusing with that type of thing!)
I just googled it and it seems that there are different levels of sprain, (google will answer 75% of your questions)
maybe when Girl B interrupts, she'll say something like the sprain is not bad at all and it was just something tiny and minor
(once in a while, you'll trip and sprain you ankle or something, but most of the time, it heals within a day even if you do walk around and stuff, I guess that's s minor sprain?)