step 1: if shes sleeping soundly now and is reacting "fearfully" (and not just when you touch her) id wait untill morning, however first thing get her in, seen by a vet and dont take "we dont have any openings today" for an answer...
a fall like that can do some very serious injuries, pinched nerves are not uncommon and from her reaction trying to stand back up it woudlnt suprise me if she didnt at least give herself enough of a jolt to cause some swelling/bruising and tenderness.
before heading out to the vet call your frined, tell them you HAVE to take her to the vet and she will be responsibel for ALL vet bills associated with this injury, also send her an email, DATED and CC yourself on it, you want physical evidence that you told her that she is responsible for any vet costs that are a result of her actions.
step 2:
Take a DEEP breath, you panicing and worring will just freek the poor pup out...
shes going to be shaken, wowies are sensitive and dont take well to those kinds of situations, give her time, talk softly to her, be gentle and dont rush her, belive me, shell get over it, but right now she just needs a little quiet time, let her come to you rather than the other way round if possible, and reward her for calm behaviour. Shes probably not quite sure what exactly happend, all she knows is something bad happend and shes not sure where to direct her fear, give her time to settle and all will be ok.
step 3:
file a report, saying your sorry means absolulty nothing if your going to add a comment akin to "serves her right" to the end...shes not sorry...and it woudlnt suprise me if she does the same to her own dogs.
file a report, even if nothing comes of that you at least have a FORMAL report on file with the police should something legal come out of this, (ie she refuses to pay the vet bills, or theres potential serious injury, or she tries something like this again as "repeat offenders" are more likley to get comuppence on these situations)
step 4:
with a clear mind write down exactly what happend for your own records...anger has a tendency to twist perceptions, taking a moment now to make a clear account of the incident will help later shoudl things go further and emotions realy get flared.
step 5:
while at the vets explain EXACTLY what happend, and the reaction afterwards, how she was having trouble standing, balancing, screaming, seemed to be in pain ect, explain that even now shes still acting very frightend and screaming ect when you move neer here and your worried shes currently also in pain, see what the vets suggest but make sure they are very thorough, you would also like a WRITTEN report form the vet explaining their findings (injuries or not, potential future issues that might come from this ect...) and that they feel in their experience said injuries (if there are any) are the result of the incident.
you want them to keep a copy on file, you want to keep a copy for your own files and give your "friend" a copy, keep the origional vet bill for yourself and give your friend a copy of the bill along with this vet report.
keeping your papers/documentation in line and correct will help should things progress legally.
step 5:
call your "friend" and tell them you cant be friends with ANYONE that would do that to any animal let alone a tiny puppy...and point out that she didnt even show remorse, then, beyond any legal stuff, giving her bills ect id cut of most of the contact with her completly.
people that can do that to an animal are scum, plain and simple.
theres a huge difference between puching and animal off you, a reaction ect, and scruffing a dog and practically throwing it at the ground...
it sounds like this person needs anger management counceling or something and id be worried for her own pets.