I'd say there is a subtle difference though. "About as tall" implies that she's around the same height, could be a little more, could be a little less (in fact, "more or less" is suggested for "à peu près"). I'd say "almost as tall" implies that she's a little less tall, but close.
That all depends on what you think determines correct English. If you believe correct English is based on the prescriptions of grammar books, independent of whether or not those books are making an attempt to "generalize the systematic use of the language, not the other way around" and are successful in doing so, then you could well be wrong. And I think you are. Consider:
"...it mainly has to do with Robert Lowth's victory over competing authorities (for example Priestly) during the period in which the first attempts at authoritative English grammars were being written in the 18th century. Lowth, like many of his fellow grammarians, was frankly revisionist in his aims and said that he intended to make English better fitted for its growing role in the world. In particular, he was one of the most important people to insist on a series of rules -- in particular, condemning split infinitives, dangling prepositions, and insisting on predicate nominatives, including "It is I!" (Priestly argued for the opposite view.) His reasons for doing so were more or less entirely modeled on how infinitives, prepositions, and nominatives are handled in Latin; since he was himself a classics scholar, and almost all the written grammars available at the time were grammars of Latin. They persisted through the Victorian school system, without making much impact on the actual daily use of the language, because the people in charge of writing English grammars were very largely people who had little or no training in the history of English or historical linguistics, but did have an educational or professional background in Latin or classical Greek.
But the problem, besides the fact that English is not Latin, or even a descendant of it, is that the rules don't even make sense in English morphology. You can't split an infinitive in Latin because infinitives in Latin, unlike in English, are single words, so it's not just "mistaken," but literally impossible to do it there. English allows you to easily split infinitives, precisely because English infinitives involve an auxiliary preposition. Prepositions can end a sentence in English just as they can (and often do) in German, and sometimes they have to. At least if the word order is going to even remotely make sense. And you have to use "ego" in Latin because in Latin there is a systematic and pervasive case system, and word order is almost entirely irrelevant to the meaning of the sentence. English -- like some other languages, including French -- used to have a similarly free word order, but then got rid of it in the transition from Old to Middle English; and the so-called "objective" pronouns are now specifically, routinely used based mainly on their position in the sentence, not on some long-dead case system that has been extinguished in every other part of the language. (Hence why in French you would say "Je vais au bijou," but "Irene et MOI allons à la bijou.")"
"Grammar, when done right, is an account of the systematic, spontaneous and accepted usage of the language, as well as the study about how the systematic rules that govern that can best be used to express meaning and avoid ambiguity. That's a perfectly well-defined intellectual discipline; it's an area of empirical study and careful reflection, which it is perfectly possible for people to argue about, and which it is possible to make claims about which turn out to be true, or false, of the language as she is spoken. If you predict that people using modern English will say, or accept, "It is I!" in preference to "It's me," except under some very limited conditions, then I am specifically saying that you are wrong about that, and that the latter is not just equally good; it's actually preferable, i.e. more correct." -- Charles Johnson
To echo that, if your rule predicts that people using modern English won't systematically, spontaneously, and routinely say, or accept, "She is about as tall as me," then you're wrong about that, even more so in the past 35 years or so. But it was just as wrong when Shakespeare wrote Cleopatra saying of Octavia, "Is she as tall is me?" in Act III of Antony and Cleopatra.
Well no, she isn't correct! Or rather, she's no more correct. It's "as" as preposition versus "as" as conjunction (with or without ellipsis). Both can be used, with the conjunction use considered more formal - see for instance "The New Fowler's", or http://sesquiotic.wordpress.com/2010/11/11/is-she-more-knowledgeable-than-him/ (talking about "than" rather than "as" but the idea's the same).
I'm curious to know how you've gotten this far without getting used to the format that duolingo uses. I mean, far be it from me to be able to say what can and can't make you angry, but... This is how duolingo works!
It's just not in the model to have exhaustive lessons. If you want them, you want a completely different site. May i suggest about.com? :)
My first time seeing 'à peu près' ... if you are also a newbie having problems going from the literal 'at little near' to the expression 'about' this site explains it well:
Avant d'en venir aux insultes, could you please consider this:
"à peu près" (not peux) means "about/around/almost/pretty much/nearly/more or less/roughly/approximately".
"aussi grande que" is indeed "as tall as".
Therefore, "à peu près aussi grande que" = "about/around/almost/pretty much/nearly/more or less/roughly/approximately as tall as".
The whole adjectival phrase describes "she". She is X. X = about as tall as me. "About as..." and "...as me" only serve to change "She is tall" into something with the appropriate relative meaning. It's the same in English and French, but in French that means that "tall" is feminine.
"a peu pres" is an expression that together translates into "nearly" or "almost". There are many other such expressions like "a peine" (hardly) which just need to be understood in context.
As with every language there are lots of English examples like "I'm wiped out" for (I am tired).