Sounds like an annoying situation. I'm sorry you're going through this. Your post is kind of short, so I don't really know what advice to give you. Here are some quick thoughts:

1. Ignore what the grandparents think. You can't control it, and the more you defend yourself, the more you'll just drive yourself crazy.
2. I'd start rewarding kids that do chores and ignoring those that don't. For example, you could make allowance based on chores. If you're not comfortable with paying kids to do work (I'm not), then you can find other ways to reward the good behavior. Make it a fair system, that way she can choose to participate or not.
3. She's becoming a teenager... and teenage daughters are the worst! Some of this is normal. I have friends who actually cry over what their natural teenage daughters are putting them through, it's a rough time. Try to remember how you were as a teenage girl and that will help you take it less personally.

Good luck!

IMHO the only way to address the whiney Skid is to turn up the heat when she whines. If she does not do her chores without whining..... have her write 10K sentences about that infraction.

"I will do the chores assigned to me. I will do them well and I will do them without complaining. Because I failed in that reasonable behavior I have to write ten thousand sentences in perfect handwriting with no punctuation or spelling errors."

She has to write 120 to 180 sentences per hour (depending on the length of the sentences to to written.) and failure to meet any one hour quota or if there is one mispelling, one punctuation error, or one messy letter it resets that hours cound and adds that quota to the total number of sentences to be written.

This does several things. It punishes hte kid without turning chores into punishment, it removes the kid from the presence of the rest of the family so those who behave appropriately do not have to be subjected to the bullshit of the illbehaved spawn, and it keeps the message of the inappapropriate behavior front and center in teh kids mind for hour, after hour, after hour.

12 is in the optimal range for this punishment. We arrived on this when SS-23 was 8yo and he wrote countless sentences from age 8 to ~13.

To this day he cringes if we mention sentences. }:)

There is also a beneficial long term influence of sentences. My son has amazing handwriting.

The message is that if SD-12 is whining when she should be working she can STFU, be quiet, be separated from eveyrone else, and work when everyone else is done with their chores and enjoying themselves even after she completes her chores.

Lather, rinse, repeat.