My Mom just died and I am on her checking account. Is the money in her account is mine?

I would act in accordance with your mother's wishes. I have my name on my mother's checking and saving accounts. Together they are a sizable amount of money at the present time. If she doesn't have to enter a nursing home, they will still be sizable when she dies. I plan on dividing the money among the heirs if it is a large enough sum. My name is on the account as a convenience and not really as an owner. My mother and father wanted their remaining assets to be divided among their children, so it is what I will do.

If it was just a small amount, I would just convert it to me after paying all the final bills. Dividing a small amount wouldn't have any meaning and wouldn't be worth the time to do it unless someone asked that it be done.

Well then, it is yours. If it was a joint account, take the death certificate to the bank and then they just do the changes.

If you are joint on the account you can close it out, without even a death certificate. The bank does not need to be told. Call SS immediately, as well as pension or annuities, as it is a major fraud to accept her payments after she passes.
While I would agree that you deserve a compensation, I personally would not risk breaking sibling bonds over a few bucks. I would be upfront about what I am taking and why, if they were absent for caring for mom, they should understand.

So sorry to read about your Mom's passing.

As for the checking account, what does your Mom's Will indicate to be part of her estate? You said "her" checking account.... was that account used by you to pay for her care? If so, I would assume it is now part of the estate.

All assets to be split equally. I always say her checking account. I used it to go grocery shopping, pay her bills, I took care of her. She couldn't get in and out of bed by herself. I would be there morning noon and night. I did it all for her.

Checking account is not listed as part of the assets.

If it's set up to be payable on death (POD), then it's yours. However, any automatic deposits (SS, pension etc) is part of the estate so you need a different account for those.

I am not a professional, this is just my take on the matter.

Are you a joint owner of the account, or just have authority to write checks? Whatever, follow the above advice on SS or pension money.

My mom has had me on her checking account for years and her statements in the mail say "JTOWROS " after my name, which is for Joint Owner With Right of Survivorship. On my own business checking account (different bank) my husband is listed the same way. In both accounts, one person is basically using the account, but the other person is there "for when" one dies. Nobody would set up their account in this manner, unless.they really positively desired that joint owner to have all.the money, after they die. So yes, the account is now yours, and the siblings who were not specifically named, are not to receive any of it (unless you are feeling generous).