How do you know which "Ona" (singular feminine or plural neuter) is being used? Is "kratka" the key to determining this, and is it singular or plural? ..am not good at this at all!
The clue is "nejsou." Since that's the third person plural form, "ona" can't be the third person singular feminine version. And, yes, it can all be VERY confusing, especially when you're (1) not too far into this yet, or (2) far enough into it to start getting REALLY confused... like me! :-)
Group if women would be feminine (ony). This is neuter, so it can be a group of ropes (lano). Or it can refer to the never-ending restrictions on the Czech motorway, they really aren't short. :-) And a restriction (omezení) is neuter.
Maybe I am weird but I have probably never heard anyone say this sentence in Czech xD It is good practice though.