まる子のタコ風船は、七夕飾りのとがった部分にさわってしまい、ものすごい音ではぜてしまったのだから運命とはわからない。
Maruko's octopus balloon ended up touching a sharp part of a Tanabata decoration and burst with a tremendous sound, so ????
I'm confused about 運命とはわからない. I thought とは was used when giving a definition. So this would be "..so Maruko doesn't understand (the definition/meaning of) fate".
I think this translation must be wrong because I don't see how it can be a consequence (から) of the events described.