...screened you and you passed her screening? If so she may be a provider that is OK discussing specifics once a potential client has passed screening. I usually have those kinds of discussions by TER PM but I'll use e-mail from time to time.
It's better from your side to never initiate a conversation regarding any specifics such as she mentioned even if you have passed screening because you don't know if she is OK with it or not. Many providers are not OK with it and will cut off contact at any point. Some are OK with it.
If you had passed screening then it's not a big deal that she brought it up.
If you had not passed screening it's iffy whether it was OK or not. If you did your research and you're confident she is legitimate (ie. has many good reviews many of which are by established reviewers, isn't using stolen/fake photos on her site or in an ad,doesn't have various phone numbers connected to various sites, ads or agencies) it isn't likely she is LE and she probably isn't a bait & switch or a rob threat.
No it isn't a standard thing. There are many accepted ways of doing things but there really is no standard in this business.
If you're not comfortable with that level of explicitness then you shouldn't do it and stopping communication was a good thing. You have to do what you're comfortable with.
I know I didn't give you a definitive answer but in this endeavor there are few definitive answers.
Are you using e-mail that can't be traced to you? Are you especially careful about not leaving things out for otheres to see? Discussions like this on your company e-mail or your regular e-mail are not a good idea. Beleive it or not some people actually do that.
Be sure you've done everything you can to protect yourself. Then if you're sure she is legit there shouldn't be a problem with her question. Remember don't do anything you're not comfortable with regardless of how legit you believe she is.