If I tell that I don't appreciate being judged, I'm afraid she'll really think I'm not a good Christian. I can no longer share my deepest feelings with her like I used to because I am constantly afraid of looking bad to her. She has a child of her own now and will compare how she is raising her child in a more Christian environment than I am raising mine. Both of us take our children to church on a regular basis. She is a very sweet person and gets her feelings hurt easily. So I don't know how to compassionately approach this with her without causing conflict.
You can start by stating that God that has placed this on your heart to tell her this... because it may help her to relate. Its called mirroring. Of course don't do this if you don't feel God is calling you, but it seems he could be from what you have said!
Don't worry about hurting her feelings, because that is NOT your intent. You really don't have any control over that anyway.
Start out by complimenting her on something, and then just go into the meat and potatoes of your issue. Remind her that as Christians we are to show Grace towards others, and you hope she receives this with grace since that is your intention.
There really isn't appropriate for her to be telling you that she is raising her children 'more christian' (whatever that is), and pointing out things you could be doing 'more christian'. Its just not needed, and YES that would be different if she felt you lacked tact and integrity or what have you. Doing this different isn't sinful - its because we are all custom in God's eyes and how he made us. YES of course a matter of opinion as well!
Its okay to approach this, and she should take it as it was intended. You can't hand out opinions like she is doing, without being able to receive it as well.
Sounds like she may just be a bit over zealous! She may learn that being faithful to God's word is awesome and as it should be. She also needs to respect and accept people and their differences as well. lol going overboard in youth I think comes with the program it seems!