German Kerber squandered four set points before losing the opener and faltered again when serving for the match at 5-4 in the third set before steadying herself to take the title.
"I think this one is really special for me because it's the first title on grass for me, and here in Birmingham I had a great week," said Kerber, who reached the last four at Wimbledon in 2012.
The world number 10 said victory in Birmingham was the perfect preparation for Wimbledon which starts next week.
"My goal coming to Birmingham was to get a lot of matches, and now I had my fifth of the week, so it couldn't be better preparation before Wimbledon," she said.
"I'll just enjoy the day today, and we'll see what comes next, and we'll see what happens there."
(Reporting by Martyn Herman, editing by Ed Osmond)
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