maestast is the contracted form of maesta and est that have undergone crasis metri causa. Here in this mix of verbiage lies your hidden est, so as to produce a non-elliptical form of the perfect with allocuta.
The OWC translation is pleasant in English but does slightly alter the grammar of the sentence.
If we take it with the preceding line:
ibi maria vasta visens lacrimantibus oculis,
patriam allocuta maestast ita voce miseriter.
I haven't read LXIII, so I had to check context, as I suspected maesta might be being used substantively. The general consensus is that a female is speaking here, but because of the crasis it cannot be told whether maesta has a long or short a. Based upon Catullus' affinitiy for qualifying as many nouns as possible, I imagine it to be a long a of the instrumental ablative. Thus:
There, gazing upon the desolate seas with teary eyes, she addressed her fatherland thus in a pitiful manner with grief-stricken voice:
and oratio recta follows.
There appear to be some interesting manuscript variations upon the latter line.
Hope this helps,