Have you been palpating her? She may just not quite be ready yet. Rather than introduce a new male to her, you might try putting another male's shed if you have one. If you still have some decent time before her follicles are to the point of no return, I'd probably just try again in a couple weeks. I'm not doing pairing this time of year yet, so I don't know what kind of seasonal cycle you have them on if any.