That instructor should never touch your resistance, only you are in charge of that- it's your ride not hers.
In real life situations I never stand when climbing either but I do in spin class. Spinning is a little different, you'll improve but you just overdid it this first time.
The standing/sitting/standing sequences are called "jumps". Do what you can but never feel you must do what the rest of the class is doing. If you need time to recover, take it.
And try another instructor too. Each one is different.