Will you give your help if you were me?

There are many incidents occurred in the past months leave me in dilemma on whether or not to assist my girl whenever she asked for help.

Incident One (Happened this morning)
My girl was playing by herself happily. She is quite good in putting stories she learnt from books or video or nursery rhymes into action. Story for this morning is "London bridge". She laid two beach straw mats across the coffee table and sofa. She then used some puzzle pieces on the mat between the gaps of coffee table and sofa. As the mats are not secured to anything, the "bridge" fell. She then get very upset and made a big fuss over it. I then asked her could I help her to build a more sturdy "bridge". She said yes.

When I was half-way through helping her, she all the sudden complained loudly saying non-stop that I did wrongly. I asked her why but she couldn't tell me. She just keep saying I did wrong. I was pretty upset and walked away.

What would you do if you were me?

Incident Two (Happened this afternoon)
Recently I brought a circle puncher from Amazon. My girl was excited and wanted to play with it. She has been punching circle herself using this puncher then. But today she asked me to help her to punch circle instead of her doing herself. She said she was doing artwork and needed circle. We were doing it happily and all the sudden she clamored her unsatisfaction over the paper I punched.

I then asked why but she just keep saying I did wrongly. I then told her to do herself.

What is wrong here? I wonder why. I know she is going through emotional growth and get very sensitive sometime. But how could I make it better and avoid this happened again and again.