Yes, a woman can get HIV through a single act of unprotected sex with a person who has HIV. If the husband did not have HIV, then he could not give it to his wife. If the husband tested negative 10 weeks after sex, it is not very likely that he had HIV at the time when they had sex. (There is a very small proportion of people who do not test HIV-positive until 12 weeks after getting HIV, so it might help to test at 12 weeks if the couple is quite concerned about HIV.)
Ejaculation inside a woman will increase the chance of HIV transmission. However, there is also HIV in “pre-cum”, so HIV can be passed even if a man and woman have unprotected sex but he doesn’t ejaculate inside her.
The best way for the woman to know her own HIV status is to test 12 weeks after the exposure that she is worried about.
Let us know if that helps answer your question,