And quite often, we find that something that wasn't offensive yesterday can very well be offensive today.
First, being part of a minority group and claiming offense gives you a lot of power to inflict damage on others. You are leveraging both, the legal system and very strong social stigmas. There is a reason why you are granted this power, but with power comes responsibility. If I walk on a sidewalk and bump into someone, I say I'm sorry and we go about our business. If I'm driving a 18-wheel truck and bump into someone, it's an entirely different story. We don't have a magic gauge to measure your emotional state, so we have to take your word for it. I think scrutinizing your past to ensure that what you say is at least consistent with what you do is a reasonable measure to prevent people from abusing the aforesaid power.
Second, if something wasn't offensive to you yesterday, but suddenly is today - even if I'm most sincerely trying to avoid offending you, how do I keep up with the "list of things that offend you" du jour? Do you have a protocol in mind?
As far as I've seen, people's atitudes towards crude jokes do not change in the space of a few hours. Maybe they might change that quickly if something significant were to happen in that space of time, but I doubt it in this case.
That said, I don't think this is a case of her asking for it. It's just pointing out hypocrisy, which is a perfectly OK thing to do. It's less extreme but analogous to pointing out someone who complains about domestic violence being themselves an abuser.
The whole point is we're trying to protect people from offensive behavior. The definition of what's offensive is vague at best. Common approach - if someone was offended, it's offensive - assumes that we trust victims accounts that they were in fact offended.
While context is important, it is much harder to believe that someone would be seriously offended by a joke when they make the same kind of a joke themselves. That's why the tweet is relevant.