russian grammar thrives on inconsistencies, i believe you need to just stop looking for logic in it
the prefix "про" denotes completeness of action therefore in the future tense она прочитает means she will be finished reading, she will have read through
another prefix "по" denotes an incomplete action, a try at it, therefore for the future tense you could use она почитает - she will have read a little
both these forms are perfective
however the usual meaning of this phrase isn't that strict, both simply mean she will read
from English into Russian it would be translated according to the context
that said, for both words the present singular 3d person form is читает but the verb indefinite form can receive the prefix as in прочитать and почитать
as soon as you add prefixes про and по to the verb читать in the present form it turns into its future tense form
see? yes it is, you need to just memorize it or feel it out
often the prefix in the future tense is selected on the basis of the semantics you wish to convey
я делаю - я сделаю - я проделаю - я поделаю
я знаю - я узнАю - я прознАю
я сижу - я посижу - я просижу
я играюсь - я поиграюсь - я наиграюсь
also prefixes used in the future tense often do not exist or rarely used for the same words in their present tense form, like наигрываюсь, постарываюсь, с(о)делываю, поделываю (archaic), почитываю (archaic)
forming future tense through the verb быть always results in the imperfective form, whereas the prefixes without быть always give the perfective one
sorry about the messy explanation