If the lady will not give you a reference I would not see her anymore.  

Now if you were a bad client then that would be a different story but you implied she saw you again.

Also this lady you asked via email and then saw again after she ignored the previous email about her giving a reference is she the only one you've seen recently that can provide one?  
I would just ask any of the others you've seen that are NOT her in the last 6 months to provide one

better to ask Up front vs them getting a request out of the blue (learned that the hard way).

This is a very good question as most providers view it as a chore. I find the providers I have a great relationship with and are members of date-check etc... will do it with no problem. I think a lot depends on the clientele of the provider. If she is fairly upscale she will do it with not problem because she understands it is good for business. It keeps the providers safe and vice versa.

Maybe she's worried about getting bombarded with emails?  Of course, if she doesn't want to do it she should just tell you.  I don't think it's rude to ask.  I've given references before without getting a heads up from the guy at all.

It would be rude if you just command the lady to provide a reference. Other than that, all of this is supposed to be just business. The feelings are supposed to be involved here. However, one should understand that it is about giving the lady. one is asking references, competition. I know of an atf who never replied to my favor request - I didn't get offended because I know I was taking business away from her and she knew it. Most providers do not mind giving a reference. This is keeping in mind you are not a trouble maker otherwise that is a different story.

not rude at all, actually its courtesy on her part if she's classy

enough to do it.  Before I kiss my lovers goodbye I always remind them that I am happy to be used as a reference.  I am very happy to help other providers feel comfortable with you and so you two can have a great time.  This industry is about having fun.

Thank you all for your responses. Doing the right thing and being respectful is tantamount to participating in this hobby - assumptions are somtimes or most of the time, not the truth. I understand the topic of references can be sensitive for obvious reasons and also can be used as leverage. Sometimes good sometimes bad. Perhaps we can't avoid the injection of our own personal feelings because the question requires us to confront our own basic core, and that is: to share or not to share. And after all this is a business. How we go about it makes the difference. The same goes for us clients.
Again thank you all for sharing.