AITA for refusing to financially support my sister because she chose to become a single mother?

I (32M) have a sister, Emily (34F), who has always wanted to be a mother, but she hasn't been able to find the right partner. After years of waiting, I suggested she consider IVF treatment. I even helped her research the process and find clinics. She loved the idea and decided to go ahead with it.

Emily had the financial means to afford IVF on her own, but it meant she had to cut back on creature comforts and luxuries for the foreseeable future. Two months ago, after her fourth round of treatment, she got pregnant. The whole family is very happy for her and she's happy too. She didn't expect it to take so many rounds of treatment, though, so the bill ended up higher than she was prepared for. She does have enough money to support herself, but not very comfortably. She asked our family for help so she wouldn’t have to make even more sacrifices. Our parents are retired and living on a fixed income so they can't contribute much. This leaves me as her main source of potential financial support.

Last week Emily sat me down and asked me for money. I have no issue with people choosing to be single parents if they can afford it. But I don't believe it's fair to ask others to finance such a personal choice especially when there are significant long-term financial commitments involved.

I have a wife and a newborn son. While we do have some extra money, we're using it to keep our own little family comfortable and save for a bigger house (currently live in a single bedroom condo). I told Emily that I wouldn't be able to help her foot the bill.

Emily was heartbroken and furious. She argued that family is supposed to support each other and that I'm being selfish and judgmental. Our parents are also upset with me, saying that I'm not being a good brother. They think I should help her because she's family and this is her dream. They're especially upset because it was my idea and I helped her research it. I offered to help Emily by letting her eat dinner with us nightly since she lives nearby and letting her use my car which is cheaper to run since it's electric. She said that's not nearly enough.

I have my own family to think about and financial goals to achieve. I feel it's unreasonable to put myself in a difficult financial position for something that is Emily's personal choice, even if I initially suggested it. So AITA for not supporting her financially?

ETA: My sister is a homeowner with a slightly bigger house than mine, making slightly more money than I do. She can absolutely afford a child. She took from savings to pay for the fourth round of IVF and is rebuilding it as fast as possible by not spending. It isn't like she didn't budget, she just doesn't like being frugal. She also did take me up on the offer to temporarily trade cars and eat dinner with my family nightly. IVF was not my first suggestion. She wouldn't adopt because she wants a biological child. She did not use donor IUI because she wanted PGT done to ensure she'd have a boy because that's what she's wanted since high school. I was not involved in her treatment or consultation and I don't agree with her decision, I helped her research because I was trying to be a good brother.