Hello, and thanks for your question. Dandelions are pretty safe, but there are some flowers that are toxic to varying degrees. Pet Poison Helpline is a good resource with lots of information on a variety of potential toxins; here's a list of some common house and garden plants that can be toxic:
https://www.petpoisonhelpline.com/pet-owners/basics/top-10-plants-poisonous-to-pets/Bee stings can certainly happen, and if Dixie should encounter a bee sting, you could help prevent an allergic reaction by giving benadryl, but I'd double check with your vet before giving any medication. Here's a link to some more information on benadryl in dogs:
https://www.petcoach.co/canigive/dog/benadryl/As far as keeping Dixie from eating flowers - the best way is to simply remove any potential flowers from the spaces where she's allowed to be, and put up a barrier to keep her away from any flowers you don't want her eating! It's nearly impossible to teach our pets not to eat things they can get ahold of - it's much more effective to simply control what they have access to.
Hope this helps!