Is a female garter snake more aggressive then a male garter snake?

They can be, especially if they're gravid - and I speak from experience !

Years ago, I bought a garter snake that had (wrongly) been sold as a male. Every time I picked 'him' up - 'he' would whip round and bite me ! I put up with it for about four weeks - and was about to 'admit defeat' and sell the snake on to another keeper - when I woke up one morning to find she'd given birth to 12 babies !