"Her name is long."
Arabic has its own rules for the ending sound. Whether it changes or not is according to some special conditions. For examples:
(1) In the nominative case, it is Damma "u" (generally).
"2ismuhaa samia" means "Her name is Samia". Here "2ismuhaa" is u because the phrase is a subject.
(2) In the genitive case, it is kasra (generally).
"min 2ismihaa" means "from her name". Here "2ismihaa" is with -i because of مِن.
(3) In the accusative case, it is fatHa (generally).
"2a3rifu 2ismahaa" means "I know her name". Here "2ismahaa" is with -a because the phrase is the object of the sentence.
Nb: they are just a few examples, one for each case. The actual numbers are more.