What to write in birthday card for boyfriend's mom?

I've been with my boyfriend for almost a year, and tomorrow we're going out to dinner with his mom for her birthday. I'm not sure what to write in the card—should I thank her for welcoming me into the family or mention how she raised such a great son? She's really funny and laid-back, so I'm looking for some advice on what to say!

What to write in birthday card for boyfriend's mom?
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