I definitely think you've made progress if she unhesitatingly eats millet from your hand
As for the biting, right about now (starting from about 6-10 months of age) is when she's approaching her "teenage stage" where she's going to be more moody and withdrawn as her body adjusts to the hormonal changes
Also, she may soon be starting her first moult, which can also contribute to moodiness and biting. Either way, it's important to look at her body language closely when interacting with her to ensure she's comfortable with what's going on, in addition you should ensure she has her space and try not to put your hands in the cage unless she agrees
The "teenage phase" may make it seem like you've gone backwards in taming, but you really haven't. Take a few steps back to simply sitting with her and reading, etc. as well as not trying to move on to something new for a bit. Soon, she'll grow out of this stage and will be more open to interacting with you once more
As for pellets, there are many effective ways to get budgies used to eating them. Crushing them and mixing with eggfood or chopped veggies (or seed, as Therm mentioned) can help them to accept the flavour of them as food, and offering them pellets all day but rationing their seed (budgies should not have more than 2 tsp. of seed per day with a varied diet) can help them to take to pellets, too. Staying consistent as well as not giving up is the key to transitioning her to eating pellets as well as seed. Which brand of pellets are you currently using?