I soooooo feel your pain! My MIL is a screaming nightmare & because of my hubby's wild schedule, I am always the one who has to do the card & gift buying. My MIL has major issues and one of them is that she equates love with material goods. Makes zero sense to me, but that's how she is. Since we are on a very tight budget, this gets extremely tricky for me.
If the gifts we get her aren't "good enough" or if there aren't enough of them, all hell breaks loose in the whole family. She talks trash about us to everyone, then they call us & chew us out. No one in his family can listen to reason. She did this to us one year because everyone in the family got a stocking for Christmas, but she thought she should've gotten TWO stockings. No, I'm not kidding. It's ugly and I don't like being emotionally threatened into getting gifts, but that's a separate issue I'm trying to work out with my hubby. ;-)
What I have started doing to try and keep some semblance of peace is buying things all year long that I see that are super cheap (marked down) and that I think she might like. For example, after Christmas last year, a store had all their Christmas stuff 75% off. I got her a fantastic gift that was normally $30, but I got it for $7. I'll combine that with other gifts I bought in a similar way and bingo! MIL gets showered with gifts & our bank account doesn't take too big a hit.
Never miss a chance to check out a killer sale. All stores have clearance sections, especially after a holiday or at the end of a season. For example, you can get a jazzed up pair of flip flops that would normally be expensive for a steal at the end of summer, then give them to her for the next Mother's Day.
I'm sorry she reacted in such a catty, shallow, juvenile way. Unfortunately you can pick your spouse but you can't pick their family. If you want to stay married, you have to deal with the in-law cards you were dealt. Sucks, I know. :-(
Hope this helps. Best of luck to you.