I find TWD to b a generally dull and loathesome excuse for entertainment and abandoned it back in S3. I do not recall Martin-Green's character sadly, so find it hard to comment on her quality.
However, for all its many, many failings, the producers of TWD have rarely hired a poor actor. It is in fact the utter shite they have their poor cast doing and spouting that hurts the most. The show is a waste of their talents. Still, it's hugely successful so I hope they are all well reimbursed for their involvement.
Re: contracts etc... prior to announcing her casting there would have been significant contract negotiations between CBS/AMC/Martin-Green's agent. No doubt most things have been hashed out regarding how much (if any) time she will now spend on TWD and if the producers require her for their story shooting schedules will be amended accordingly.
I hope she is able to benefit from both shows, giving her the opportunity to broaden her exposure. Still, in the end ST DISCO will be the little "niche" show out of the two and she is likely to gain far more exposure from TWD globally than ST at this stage. If I were her agent I'd try to keep her going on both - as long as it doesn't burn her out of course!
Hugo - so... any more female characters on this show???