I think Rebecca said - in a figurative way - exactly what she was feeling at the time... "Dina is going to be fuming-mad that Maxie fell while on my watch..."
As for Maxie saying "Ocean", the dog's name, like many I also don't believe that it was possible given the extent of his injuries. But how does that translate into lying? If I tell you that my dog told me "See 'ya..." as he exhaled for the last time soon after I asked him not to wander off too far, to please wait for me, when I had to let him rest, would it be fair to say that my emotionally-stressed brain merely interpreted the sound in whatever way made the most sense to me at the time? Or would it mean that I am now lying to you? Rebecca was no doubt under duress as Maxie exhaled for the last time (on his own). If Ocean was nearby, I might've heard his name too.
Another possibility is that Ocean might've in fact been involved in some way, perhaps running between Maxie and the railing as he tried to recover control of the scooter... And, if Maxie yelled-out "Ocean!" as he lost his balance and vaulted over the banister, Rebecca could've heard the word "Ocean", remembered it, and, under such stressful circumsntances, simply been confused as to when exactly Maxie actually said it. Witnesses to tragic events are never to be trusted 100%, regardless of the circumnstances, but specially when under severe emotional duress.
Spreckels Mansion property was on Ocean Blvd. Can we absolutely rule out Max may have been mentioning the street?