If Marvel decided to let Peter Parker have child in main universe...

[Yvonmukluk]

I think you could make Mayday permanently in 616 work, without her being around Peter.

Her not being a infant anymore & She is not in NY or the US for the matter. I'm thinking She is living in Europe or UK.

Essentially retcon one more day. Have it so that Mayday didn't die from being poisoned by Osborn assassin or wasn't erased by Mephisto from history.
Instead she survived was given up to be adopted and grew up in far off place. Be a Hero with an European team.

Even after an eventually reunion with the Parker. Mayday lives separately being a hero in another part of the world.

If she's living in another part of the world and having nothing to do with her family, what's the point of her even being Mayday and not an original character?

[Steel Inquisitor]

If she's living in another part of the world and having nothing to do with her family, what's the point of her even being Mayday and not an original character?

Just add her to the Spider Family.