she would always maintain her motivation as kind. Yes, it's quite a clever one, this. Because who would find something negative in such a kind gesture? What sort of daughter could be cross with her mother for sending lovely flowers with such thoughtful thoughts etc?
She has you stitched up like a kipper op because ostensibly you'll look churlish/ungrateful/silly if you object or say anything. You know she's bullying you, and she knows she's bullying you.
The fact she doesn't particularly like your DH is interesting. If you and he did celebrate your anniversaries and he was the type to want to buy flowers for you, her big expensive flowers would be even more inappropriate.
She has taken over your wedding, and is monopolising your anniversary.
Perhaps this year, it's time to put an end to this. When she phones the first time, just say something like 'actually I'd really rather you didn't.' Then if she asks why not, you could say 'because it feels like you are taking over and if anyone should be buying flowers on our anniversary it should be DH or me'. Then if she sends them anyway, write a 'thank you' letter reminding her that you asked her not to and saying that you have given them away and will do so if she does it again.
If she has a strop, then so be it. You don't have to be held hostage to her strops anymore. If she stops talking to you for a bit, think of it as time off 