what to do about a Pathalogical lier?

my husbands ex must be a pathalogical lier! my husband is at his wits end they have a 6 year old girl together, she manipulates her too as well as lies to her for no reason, she calls my husband and says remember we talked about changing nights and hes like what the hell no we didnt, but this happens at least once a week, (they have her half time but she mucks him about) she gets caught over and over again lieing but she covers it up. She hates me for some reason i dont even know why, on my birthday their daughter had the whole weekend of dance shows and his ex rings and said we will go to one each it was really expensive so she says iv booked on the sunday so you will have to go saturday which was my birthday anyway we went on my birthday adn then she turns up to drop her off to me and said to her daughter ok ill see you there, i tell my husband that shes (ex) going he rings her (ex) and shes like oh no i lied to her (daughter) becasue she was upset that i (ex) wasnt going (she (daughter) seemed fine to me!) anyway we get to the show and shes (ex) there with her whole family who had all along booked the tickets! this is just one story out of the many where she lies so badly and gets caught and creates further lies. Im on here today because she has been lying big time this week including today so i was on here looking up if she actually had a problem and i found that there is a condition called a pathalogical lier, sounds like she could have this which is a big problem! but what im asking is what can we do about it? carry on living with this crap or???????? my husband has had enough seriously considering just ignoring her but she goes out of her way to make our lives hell! what to do???