Please answer only if your sure!!!!!!!!!!!!!!!!!!!!!!!!!!…

ok i have a staffy x aussie bulldog (Tasha) and a neapolitan mastiff (wilson) and tasha is on heat and i have seen wilson trying to mount her and i have seen tasha mount him she stands there while he tries shes smaller then him and she has had a litter before but there father was a staffy, what are the chances she will get pregnant i don't want her to otherwise she will need a c-section!!!!!!!!!!! HELP!~!~!~!