First, have you considered that the mother's first language wasn't English? Maybe you overwhelmed her a bit. Most of my friends are hispanic, and while some of the men speak fairly good English, most of the women speak NADA. I'm not stereotyping anyone, either...this is just my experience. The last quincenera I attended had family, friends, church members, and more, and that girl's mother speaks no English.
At the last one I attended, I went to the church service but NOT the party, but these are people I go to church with and I don't actually know their daughter very well and my children are much younger. The church service MAY be more for family, I'm not sure, but she would be expected for the party for sure!
Use your own discretion for the gift. In their culture, this is a girl's transition to womanhood, and it IS like a wedding...just wait until you see pictures of this event. Thousands and thousands of dollars are being spent on this party, I can assure you. However, that doesn't dictate that you need to spend a huge amount on a gift. If your daughter wants to give her money, then give her money. That's up to you.
Daughter needs to be dressed to the nines.
(Want to second what Momof2 had to say, and it's CERTAINLY not racist. Every invitation I've ever received to a Mexican party...birthday, wedding, anything...has been given the day before the event or the day OF. I swear, my neighbor invited me to her baby shower 2 hours before it was supposed to happen, and I had to run out and buy a gift! You shouldn't take offense.)