Sorry to say this but a short prison stint will likely boost her career if anything. Her rabid "so amazing mum" fans will stick by her. A lot of the wider public who don't follow showbiz maybe only associate her with page 3, being a "good mum to a disabled son" and possibly a drink driver, a prison sentence would likely dim the wider public's view of her a bit but not significantl, I think. The "good mum to a disabled son" bit gets her out of a lot especially among the wider public who don't know all the gory details of her life that get discussed on here.
Prison - well no publicity is bad publicity is bad as far as I'm concerned, unless it's something involving sexual offences or a serious assault or a murder, the celebrity I believe would be completely blacklisted. Most people hate drink driving but I don't think a prison stint for it, or the Michelle restraining order offence, will get her blacklisted sadly. Plus she'll play the Harvey angle to death and as I said, some people will excuse almost anything if they see you have a special needs child.