ona pocałowała ją trzykrotnie - why not ?
It's ok but they probably didn't think about this answer.
The subject ("ona") should be omitted unless you want to emphasize it. "Trzykrotnie" sounds pretty formal and would rather translate to "threefold/triply".
'Trzykrotnie' is perfectly OK. And 'ona' CAN be omitted but is also all right in this sentence.
Pocałowała is not recognised as a word in my phone's polski dictionary. It wanted to alter it to pocałować, but thats as close as it would go. Any thoughts why?
My Polish phone dictionary (SwiftKey) is the best one I found, but it still misses a lot of forms, especially past ones.
Ona ją pocałowała trzy razy.
Seems acceptable, added.