Thank you :P
Sarah couldn't have got my massage. Otherwise she would have replied.
I wonder why Sarah hasn't replied to my message. I suppose she might not have got it.
There is no point of speaking English if you don't know the right pronunciation.
I need something to open this bottle with.
I made a couple of changes to your phrases. The correct grammar is "have gotten" which means "to receive".
"Sarah couldn't have gotten my message."
"I suppose she might not have gotten it."
Anyway, hope this helps.