I don't like how my girlfriend helps with the washing up
Isn't that a good thing? Why don't you want her helping with the washing up?
I can do it by my self and I don't like how she washes the plates and cups and ruin them.
You should be grateful that you have someone there that wants to help you. Gratitude promotes optimism and helps us to develop a more positive outlook on life.
Ever heard of strength comes with weakness. I don't want her to ruin my plates and cups.
Even if she doesn't do a good job, it should be the thought that counts. I can tell she cares for you and what you can do is to teach her how to properly do it instead of resenting her for helping.