As others have noted, each school's curriculum will dictate when students are formally taught various skills.
A student performing a skill only previously practiced in skills lab may need lots and lots of guidance. The dummy's labias don't flop around, the dummy's have no extra body fat, the dummy's legs can spread very easily, the dummy's don't move or talk or feel, the dummy's urethra is an obvious hole... and even if you've done one, the next one might be totally different as human bodies are unique. After you've done many of them, then you can feel more confident that you can perform it correctly on just about any shape or size person. Unfortunately, many students haven't even had the chance to watch such procedures in practice. Maybe once or twice if lucky. After all, what patient wants 10 nursing students surrounding the bed to watch them be cath'ed? And how many nurses want to be watched by a bunch of questioning students while performing said task?
Many students come out of school having only practiced such skills once or twice over the course of a year or two, so even if a student learned a skill first semester of their first year, it may have been several months since they intensely practiced it. If they didn't know the night before that they'd get to do a cath, they might not feel confident that they remember every last detail... and in skills lab, instructors would often critique students on the smallest difference in procedure, even if it didn't compromise the clean technique - so a student might feel very nervous and intimated to perform a straight cath alone without thoroughly reviewing every last subpoint of the precedure before performing it.
It sounds like you may have run across a student who either couldn't or didn't want to perform a straight cath. I can't say what her particular reasoning was and if it was valid or not.