Why is my mom always trying to make me do stuff she can easily do?

if you use the shower you should clean it a couple times a month while you're in their.

get a box or basket teach grandkids to clean up

talk to your mom and stop cleaning up after her.

Ask her who dirtied it?

You know when there is a problem when she makes you clean while she is yapping on the phone, texting, watching TV, etc.

If you live with her, you should do your part to keep the house clean. If you don’t live with her, tell her to do it herself. I assume her grandkids are from one of your siblings. If they’re yours, you should be cleaning up after them. 

If she's got grandkids you've been there too long.

Here is a thought to change the dynamics of the situation.

Instead of waiting for your mom to tell you to do something ...Ask her what you can do to help her out.

I know it goes against positioning yourself in the household, but it will change the atmosphere and put you in charge.  

You are living in her home.  Unless you pay rent, you do what she says or you move out and do not do what she says.  Keep talking back and she will tell you to pack up.  If you are under 18 she will drop your *** at social services and tell them to deal with you.

I'd say just clean.  It  is easier...less drama.