So, I go to my friends barn ocassionally with her and we ride. But, she always says that she can't get her horse to keep going when she's posting and I got on and her horse did it perfectly. How do I help her without sounding like a "know it all"?

i would just go out one day, ride him a bit, then show her excactly what your doing to keep him going- how your leg is always hugging him and positioned next to the girth. Not being able to keep a horse going is a pretty common problem beginer riders face, and she probably just needs to learn to always keep her leg on him.

sounding like a know it all is different from her aknowledging that she has a problem and you offering advice.
Just tell her, demostrate if you have to.

Ask her if she wants you to help her.If not then she may need to learn it in her own time.Or she might want you to show her what she is doing wrong and help her.Be like I noticed this problem.I think I might know a few things to help.Do you want me to help you???

^ i agree 100%! afterwords give her advice and tell her wat she can do

Yeah, but she sooo made me mad at this past horse show. She got furious at Cashew when she did the trail class, because Cashew wouldn't do anything, BUT she doesn't even spend time with her!!! She hadn't ridden her since the last show (3 months) and then twice before this show and expected her to be perfect! It makes me sooo mad! She doesn't appreciate her at all. And then she asked what to work on and I told her, "you need to work on trot poles" she said "she's fine with them" I told her "you need to work on the bridge" she said "oh she's done it before." I told her to "work on the p/u carry" she said "she doesn't care about that" I told her to work on backing" she said "she backs fine". I mean WHY ASK IF YOU DON'T DO IT! OMG she makes me sooo mad. So apparently this has turned into a bit of a different problem. It's worse.

BTW. This is Horseluv90. But for some reason I can't log out of my friend, Haley's, account to post mine. Sorry for the confusion

You two need to sit down to two cups of milk and some cookies and talk things out.Tell her I am trying to give you advice but you are not listening.It makes me mad.You don't ride your horse for soooo long in between shows and you expect her to be perfect.I think you need to pracice more and maybe take a little advice.