Daughter Is Being Really Mean to My Mom

Lola is spot on. Your daughter is not happy that you have been absent (has there been more than just the one business trip?) and that grandma has been in charge of her. Some of the acting out and unhappiness is inevitable as she tries to adjust. Some of it could be exacerbated by perhaps Grandma having different rules than you do when you're not there. From experience with my own daughter (who is a rule follower and does NOT like to get into trouble of any kind), know that, just because she does what Grandma tells her without backtalk, etc.. doesn't mean that she LIKES what she is expected to do. She may also very much resent Grandma doing things with her that YOU used to do with her. Are there "special" things that you once shared that now Grandma does with her instead? Of course there are. You may not think of them as "special".. but that is how it is perceived by your daughter, particularly now that it isn't just you and her. Grandma (in your daughter's perspective) is interfering in your relationship.
Please be sure (if you aren't already) that you take time to spend alone with your daughter daily. Have time that is just you and her, no grandma. Bedtime is a great time for this. Have her say goodnight to grandma out in the living area (not grandma coming into "her" bedroom)... then you and she go snuggle up with a book for her bedtime ritual... just you and her.
Also... if Grandma is now her caregiver (and is unemployed)... she probably isn't spoiling her like grandmas tend to do, and your daughter is probably accustomed to from her grandma.
I know that my kids' attitudes toward my parents changes when I have left them in their care for a day... totally different than when they are visiting only and aren't the "authority" in charge of them. And actually, so does my parents'! (They are less tolerant).
Perhaps you and your mom need to sit down (privately) and discuss "parenting" strategies and routines. Make sure Gram isn't being more strict than you think. No matter how much we love our kids (and grandkids) I think our tolerance for them is used up faster as we age.. unless your mother is a TOTAL and COMPLETE SAINT!
I am only 40, and I have less patience with 3 & 4 yr olds, even 5 & 6 year olds than I did when MINE were those ages... and it wasn't that long ago.... mine are only 8 & 11 now. So perhaps letting Grandma have a breather from childcare (when you aren't around) - if it's possible - might help some too. Be sure that your daughter gets to participate in playdates and other fun activities that she was doing before Grandma arrived.
And keep praying.
hth

"grandma moved in and everything changed"-that is what your daughter is thinking.
you need to set some rules that you and your mom will go by. for example if your daughter disrespects her she is to be sent to her room. then she needs to apologize etc.
this is only if you want mom to stay with you until she finds a place for herself. remember, she is helping you by taking care of your daughter when you're not around.
so sit everyone at the table and set the rules. explain to your daughter that she is your mom and that she is not allowed to 'act out.' and if she acts out there will be consequences, like take away fav. toy, get time out etc., just as if she were saying these things to you.
you also need to understand that your daughter needs to adjust to the new living arrangements.
you said she doesn't treat other relatives like this. this is easily explained: the others don't live with you
good luck

Lola and Victoria are right. This is good advice.

They get along while you are away? I doubt it. There's more to this than you are being told.
Talk with your pediatrician; get a monitor; and ask your neighbors to keep watch.

childrensbehaviorhelp.com- and yoka Reader too, right away
keep talking to both of them- you are doing a good job- really you are-k