The way that I have passed all levels on Fashion Dash has been to seat customers in the appropriate colored booths.  I chain everything.  If you have grandma, always give her her magazine first, because she takes the longest.  Fill all the seats as you can.  Turn on the radio for the waiting customers at every chance.  It doesn't break the chain.  Take all of the orders, but grandma's are always first.  Then, I get all of the outfits at the same time.  After the outfits are gone, turn the radio on.  Wait until everyone's ready to pay.  If a customer wants jewelry, give it all at the same time.  Then, collect money at the same time.  Then take all of the hangers back.  Start all over again.  I only give the drinks to the men, who get more impatient  and only if their heart is 1/2 or less.  Do that before giving out the magazines.
 
Also the order of your upgrades makes a world of difference.  Always get the faster booths first, then the comfortable waiting chairs, then upgrade the booth chairs.
 
This should help you finish the game.