"She is waiting for all morning" is not correct unless you add an object to the sentence here: "She is waiting for (noun or noun phrase) all morning." Even then, the sentence is awkward. Usually, a different verb tense would be used in the "waiting for" scenario. (Ex: "She /was waiting/ for Elizabeth all morning." or "She /has waited/ for someone to call her back all morning.") "She is waiting all morning" simply means the subject ("She") is presently in the middle of doing an action ("waiting"). The length of time she has been in the middle of doing that action is "all morning." Hope this helps!

"Waiting for" means that she's expecting something, like why she is waiting. Waiting just means that she is waiting. That's it. So the correct sentence is "She has been waiting all morning" If you want to say what's she is waiting for, as in why she is waiting, you say "She has been waiting for (something/someone) all morning." Ex. She has been waiting for the mail all morning. She has been waiting for him all morning. She has been waiting for that all morning.