OP is upset because her DD has different priorities. IMHO, she has the right to tell her daughter that she is making questionable decisions because 1) its her daughter and 2) she has been on the hook to help with the car, etc.
As for the $500 from Grandma...is it possible that DD thought an IPad would be a gift for the house? I mean you can't eat it like its expensive chocolates. You can use it at home can't you? Either DD thought it was a gift for the home, or she is one of the many twenty somethings that is only interested in #1.
As for getting the gift...your daughter's thoughts were in the right place even if her priorities are not.
My inlaws enjoy getting me gifts to make fun of my weight. When we were newly married and I was just overweight...they would buy me nightgowns that you could put a whole circus troupe in at the same time. I seriously hated getting clothes meant for the person too fat to leave the house. Over the years, I have gotten a little heavier. So now, they will get me a size 12 dress and say...I hope its not too big. I mean who couldn't wear something so enormous!
Hubby and I have birthdays 9 days apart. His Dad likes to take HIM out for his birthday. They just spring it on him when I'm not around. So one night, hubby comes home and says that his Dad had taken him out for his birthday. I thought...how special for you, but was ok with it. He then said...they got you a card. Oh so they remembered my birthday, but didn't want to take me out...Yay! Well, let's see the card. I thought it can't be worse than last year's card. The year before they had gotten me a card that said...its not your birthday until the fat lady sings...and then the inside had a fat lady singing. Well...the only thing worse is to get the exact same insulting card.
The point is...there are worse gifts. Your daughter meant no harm.
I'm sorry, you speak to these people?!

After the first time, if no groveling apology for being moronic twits was forthcoming, I'd say you should have just not gone near them again!