This is likely a situation where not remembering "such a text" is in reference not to memory, but to customary or standard expectations.
It most likely means that she has never read a text that was so different from her expectations. That is implied by using the word 'such.' It has a dozen or more meanings, but here I'm defining it as "of so extreme a degree or quality."
It's fairly common to use 'such' in that sense in the construction, "I don't remember [gerund] such a [noun] before;" e.g., "I don't remember seeing such a fight before," "I don't remember hearing such an argument before," etc.
And in this case, 'before' is used as an adjunct: it is not necessary to make the clause or sentence complete or grammatically correct, but it adds extra meaning. In this case it connects earlier events to the moment of speaking. You're right that it can be removed, but that doesn't necessarily make it awkward or needless.
In this case, it seems to be saying "She doesn't remember reading such a [stupid, confusing, etc.] text before [this moment in time]."
The implication is that this is one of the most unusual texts she has ever read.
M-W - Before
M-W - Such
Cambridge Dictionary - Uses of 'before'
Cambridge Dictionary -Adjuncts