What's the possibility of Nessie being a plesiosaurus?

Well, in most descriptions of Nessie and theories, she's thought to be a plesiosaurus. But how likely is it. If Nessie exists, how is she an extinct Marine reptile? They went extinct 66 million years ago. But another thing is that plesiosaurus mostly living in seawater and loch Ness is freshwater. Well, if she is one she's either a Leptocleididae or elasmosaurus which live in fresh water. But anyways, if Nessie is a plesiosaurus, how is she still alive? How did she survive the extinction events and changes in temperature. Did she evolve to age very slowly orare there more of them. Loch Ness can lead to ocean and across the world there's multiple Nessie like creatures so maybe they've spread out and hid. Basically, she's either a mutated/evolved plesiosaurus or some type of sea serpent. What you think?

Well, in most descriptions of Nessie and theories, she's thought to be a plesiosaurus. But how likely is it. If Nessie exists, how is she an extinct Marine reptile? They went extinct 66 million years ago. But another thing is that plesiosaurus mostly living in seawater and loch Ness is freshwater. Well, if she is one she's either a Leptocleididae or elasmosaurus which live in fresh water. But anyways, if Nessie is a plesiosaurus, how is she still alive? How did she survive the extinction events and changes in temperature. Did she evolve to age very slowly orare there more of them. Loch Ness can lead to ocean and across the world there's multiple Nessie like creatures so maybe they've spread out and hid. Basically, she's either a mutated/evolved plesiosaurus or some type of sea serpent. What you think?