Well, there is that too!
The thing is, she and the Tories have had the inside track regarding Brexit so far so should have some idea what is to come from Brussels during the negotiations. And if, as some predict, it is likely to be a car crash for the UK, then would the Tories want to be the party held to account?
Politically, though her career as PM would be over, wouldn't it make sense for them, as a party, to pass the responsibility to Labour, so they would be held accountable for the inevitable fallout of a potentially bad Brexit for the UK (hypothetically assuming that's what actually happens of course!). The Tories could then ride to the rescue, get a massive majority, and probably govern for years.
I highly doubt that the actual powers that be in the Conservative party care too much about her long term career, more of the long term interests of their own party. She was never elected by the public anyway.
I just fail to understand why they called a snap election when they already had a (albeit slim) working majority in the house of commons. I highly doubt the EU leaders care how big her majority is.
I get the feeling that the Tories are playing the long game. And the more I see from May and her campaign, the more it makes me think that maybe, just maybe, this is the case.