As long as you are a service member in good standing or a spouse of a service member in good standing, then you are eligible to take the exam. Furthermore, you are allowed to take the exam as many times as you want as long as it hasn’t been less then six months since the last time you took it.
There is information on the web that states that you cannot take the DLAB again if you receive a passing grade, however this is false and not true.
Spouses are allowed to take the DLAB because in some cases, they are allowed to enroll in the Defense Language Institute with their sponsor. The military allows this only when there is available room in the class and when the service member has follow-on orders to a country that speaks the same language in which they are enrolled. Furthermore, the military actually encourages this because what better way to ensure the service member maintains their language when his or her spouse also speaks the same language
Therefore, the only thing stopping you, a good standing service member, from taking the DLAB is yourself. So remember to test early and test often.