Double her weight at 12 weeks will give you a close estimate of her adult weight. Although if she is 3.5 at 10....it's likely she'll be at least 7 pounds as a adult. Genetics goes back beyond just her parents.
She does have a lot of hair on her ears weighing them down. You shave them with clippers. A mustache trimmer works nicely. You can get one from a drug store for about 20 bucks. Using scissors trim the edges close to the ear cartlidge. Use the trimmer. to shave around her bum and that'll help with cling ons too and you can use it on her paw pads...which will make it a little better if she steps in urine.