"You have a strict mother."
Translation:Matrem severam habes.
No, of course it's correct; the whole point of having meaningful endings (an adj. ending in -am like sevēram 'has to' be modifying a feminine singular noun, like mātrem ) is to be able to allow the words to appear in a number of different sequences. They certainly don't have to be side by side. "Mātrem habēs sevēram" in my mind puts emphasis on the adjective: "You have a mother who's severe--and how!!"
An "us, a, um" adjective like sevērus, sevēra, sevērum uses 1st declension endings (like nomin sing sevēra ) for all feminine nouns.
Because mātrem is accusative, singular, and FEMININE, it must be modified by the 1st declension adjective in its accusative singular form: sevēram .
(Masculine and neuter nouns will be modified by 2nd declension forms of this adjective: sevērus , the masc nom sing, and sevērum , the neuter nom/accus sing form.)
Hope that answers your questions; let me know, if it's still unclear.