ffs the cousin has ASD
And.........???
How the hell does the cousin cope in school, or when she is playing out with friends, if someone else is called Maddie?!
Cry me a river. There is no reason on EARTH for the OP to not call her daughter Maddie, just because that is her cousin's name.
It would take a very weak, easily downtrodden person to be bossed about like this, and not call her child by the name she wants because 'auntie wotsit says so.'
The cousin needs to deal with it. It's life. And the aunt cannot demand her own way all the time because the cousin has 'asd!' FFS! 
Don't do it OP. Your aunt has made a reasonable request.
SO many names to choose from. What about Annie, Maggie, Hattie, Connie, Cassie
Oh FFS! 😂
As @greentulips said above - why doesn't the aunt rename her daughter? I am sure we can come up with some lovely alternative names.... How about fanny flo-flo, Bertha Babbles, Dorcas Malorcas, Edna, Helga, Myrtle, Betty bam bam, La la, Dipsy, Tinky Winky, Luluboo ... there's LOADS.................. 
And 'bobbly,' there is nothing WEIRD about using a name you like for your own child. What a ludicrous thing to say. It's weird to be bossed about and not call your child what you want to because of the demands of an entitled and precious relative.
Call your daughter Maddie OP, and FFS ignore the ridiculous suggestions and the 'bizarre' alternative suggestions that people are posting on here.