The gemara says that Yalta, who is famously known as the wife of Rav Nachman, showed her blood to rabba bar bar chana for a p'sak. Tosafos HaRosh points out that perhaps Rav Nachman either didn't know or was out of town. However, from the end of the story it sounds as if she ALWAYS showed it to Rabba Bar Bar Chana. It would seem from here that a husband is not allowed to pasken on the ma'aros of his wife. Tosafos rejects this possibility based on the mishna in negaim 2:5 which discusses other things a husband can't pasken for a wife, but makes no mention of this. Therefore, Rav Nachman was either not an expert in paskening on blood or perhaps he was concerned that he would be too machmir, or that she would be מתגנה on him.
The Chochmas Adam 109:6 paskens that although a husband may pasken on the ma'aros of his wife, he can't pasken on mikvah questions as he explains in Binas Adam 3 that when there is a chezkas issur the husband isn't allowed to pasken. She doesn't have a chezkas issur that she will continue bleeding forever so he may pasken on the ma'areh that the bleeding stopped, even on a hefsek tahara. But she does have a chezkas tu'mah until she goes to the mikva, so he can't pasken on chatzitza issues.