I think its because at the end of Spectre, Bond retired so M must have given the 007 license to Lanasha's character. Throughout the course of the movie she'll either die or give it up and Bond will get it back.
Ian Fleming is probably rolling in his grave at them making his womanizing secret agent a female. This is taking PC way too far.
People said the same when Judi Dench was confirmed as M.....
I had no problem with Judi Dench as M and thought she did a great job in the role. Unless they completely change the character of James Bond I don't think female agent that beds every man she comes across is going to be that popular whether or not it is okay for a man to bed every woman he comes across but then that is the was Ian Fleming wrote him back in the 1950's and 60's. I also think Idris Elba would make a great Bond.
I still think that if the whole new 007 thing is genuine, that something plot wise will have James take it back at some point, but then he'll die and the whole James Bond name will become a codename along with the 007 designation.