Simple answer: No.
Longer answer: Maybe.
From your description, it sounds like you sister has a job and she probably made more than $4050 for the year. That would disqualify her from being your dependent, unless she was a full time student; in which case a different set of rules would have to be looked at.
Your niece can be the qualifying child dependent of any relative in her household. So you sister gets to decide whether to claim the child herself or let you (& your spouse on a joint return) claim her. This assumes you & your spouse have a higher income than your sister.
One thing you can do is prepare returns both ways to see which way the family comes out best. You can use this tool: https://turbotax.intuit.com/tax-tools/calculators/taxcaster/?s=1.
You first thought might be that the taxpayer in the highest tax bracket would come out best. But because of today's convoluted system of tax credits, that's probably not going to be the result in your case.