Bfs [27M] sister [30sF] hates me because I'm [25F] technically the reason her kid isn't getting extravagant gifts from him anymore.

My bf is one those people that love giving gifts. If he loves you, he goes all out for you. Last Christmas, he gave his sister 1 grand and spent another grand on his nieces gifts. She's an only child so she definitely had a very merry Christmas! At that point we had only been together for around three months so it definitely was none of my concern/business. Instead, I set a limit with him on the gifts we got for each other and we had a great time.
So, I'm a cheapskate. I'm great at budgeting, bargain shopping, and lying in wait for sales. Bf loves it. He asked for my assistance in saving/shopping in a smarter way. I said sure, and I've helped him handle a lot of his money wasting habits. He now cooks instead of ordering out 5 times a week. :) So far it's estimated that he's saving around 200 more dollars a week from food alone.
The issue comes in when it comes to his niece and getting gifts for her. Basically, he's been the fun single uncle with money to blow. He expressed regret at spending the grand last Christmas because his niece was only 5. She's easily scared so she was terrified of the pink Cadillac ride on he bought and only used it twice. The other gifts were used for about one or two weeks then she was on to the next big thing. That's what kids do! So he asked me to tag along when shopping at toys r us and help him form boundaries/limits.
So first issue, His niece is used to saying "uncle, I want (insert toy name)" when she sees him and he'll have it purchased and ready by the time he sees her again. Instead, we agreed on one or two surprise gifts per month so she learns to enjoy being in his presence for more than just the opportunity for fun toys, since she did come to expect a gift from him. They see each other very often so he used to be getting her 8 or 9 new toys a month.
Second issue, his niece was used to telling him (cutely :/) to open his wallet and let her see, and she would then ask for money. He was never a fan of this but his sister and her husband found it funny. I urged him to put an end to that completely, so a "no" or a jokey "get a job!" Is now the reply. He still surprises her with 5 dollars occasionally but now it's an actual surprise/gift!
Third issue, I feel like this last one is what tipped his sister over the edge. His nieces birthday came and bf took me with him to toys r us. I talked him out of buying a pogo stick, a 4ft long 300 dollar children's telescope (his niece mentioned she liked looking at stars), and another bike (she has 3). Instead we settled on a 80 dollar telescope that wouldn't take up all the room in their house, and multiple moana themed toys since that's her favorite movie. As expected, this load of toys got used for two weeks. She only used the telescope three times. He was pretty ecstatic that shopping cheaper still had the same outcome!
So obviously his sister noticed that less gifts were coming into the house, and that my presence in his life was growing. My birthday came after his nieces and he ended up surprising me with tickets to see a comedian, and then the next day he surprised me with a short trip to Canada. Yeah. So his sister found out and she's super unhappy. When they spoke she asked why his girlfriend is coming before his family and if his cheapness is because I'm forcing him to give me his money. And why his niece is getting less than me because she would've enjoyed going on a birthday trip too.
She also made him aware that she dislikes me and thinks I'm a gold digger. Which from her point of view I can slightly understand if I try really hard. All she sees is gf gets a trip while her daughter is getting less extravagant gifts. But this isn't the case! I'm still a cheapskate! We have a little pizza party every time one of us manages to save another few hundred. I love saving money and seeing people save for a rainy day makes me happy!
I'd like to mention that his sister makes around 60 grand per year which is combined with the 70 grand her husband makes. If there was a less stable financial situation then I'd be contributing to his nieces care as well. But this isn't care. This is gifts. Bf makes around 65k too if anyone is curious.
So i dont know what to do here. I think she's worried I could possibly be financially using him which is mixed in with her being annoyed that her kid is getting less than she's ever gotten. I don't want her to dislike me or think I'm a problem! Is there anything for me to do here? Or maybe a script for my bf to use when he speaks to her? I'm really bummed that she thinks so lowly of me. :(
Tl;dr: bfs sister doesn't like me because I helped bf change his spending habits when it comes to gift giving. I don't want her to think I'm using/controlling him. What can bf and I do?


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Haaa...what he does for his family is really none of your concern. If he ask for your help in saving money, then do it in other areas. Don't change a man and what he already is doing. Gosh i wish the real OP would see this. You sound like a controlling gf. Just my opinion.