You have several options with this. First you need to understand that people can raise children using different parenting styles but still produce happy successful adults. Of course, if the things this person is doing are placing that child's life in danger or are considered abusive, they must be reported to the authorities immediately. If the parenting technique this person is using or not using has been proven detrimental to a child's chances for success in studies or statistically then you can give her "feedback" ( instead of criticism) If she is extremely sensitive and and does not receive differing opinions well and you want to keep your relationship with her, you have two options:
1. Write her an anonymous letter but keep your concerns fact based. Describe the behavior you are concerned with and why it concerns you. Its always good to cite scientific reasons why her parenting technique is not in the best interest of her or her child.
2. Talk to her gently in person. Approach it from the perspective that you are completely concerned for her and the stress she will face in the future if she continues to parent in that way. For example: If your friend is giving their child everything the ask for, explain that you are worried that she is setting up a life long burden of providing goodies for her kids and that giving them everything won't allow them to figure out ways to get things for themselves. If you put it to her in a way that is not critical but based on your love for her, she will receive it much better.
If you don't mind if she become angry with you, you could:
1. The next time you witness her doing what you object to you, can simply say: " I don't think you should........" and why. Don't start you statement with "You shouldn't ....." That is too attacking.
2. Email her in concrete terms with your concerns. Do not use judgmental statements such as: 'You're being a bad mom when you...." Instead, you could phrase it: "Look what I learned at this great parenting website. Studies are now coming out about how important it is or isn't that parents do ........." You can even give an example of how you have been tempted to or actually have done the parenting technique in question. She will definitely be more open to the feedback then. The worst thing you can do is give an impression that you and your children are perfect and she and her children are failures. She will not receive your advice well at all. Think about your parenting. No parent is perfect. Pick some thing you do that could be improved upon. Imagine a friend coming to you with concerns about that behavior. How would you like for them to present it? Present your concerns that way.