I'm not sure that comparing Miki to Junjun and Linlin receiving lessons is the same. Junjun and Linlin needed to speak Japanese to be able to do their job, communicate and understand with staff members whereas Miki doesn't really need to speak English and I'm pretty sure that as far as the company is concerned, her English is good enough.
That's not to say she won't get English lessons, but as I see it, she doesn't necessarily need them.