Which contraception whist breast feeding?

I have a friend who has just had baby #4, 13 weeks ago, and is fully breast feeding him. She got her period back last week, and was going to start taking the mini pill. She really doesn't want any more children, so I told her that unless she is taking it absolutely correctly, and religiously, she might want to rethink her choice, due to the failure rates of the mini pill.
What other forms of contraception is there, other than the mini pill, condoms and surgical methods, which would be ok for her to take whilst fully demand feeding a new baby?

Depo provera is ok to use while breast feeding. I've used it & still use it. Injection every 3 months. Easy & doesn't affect your supply at all :)

Mirena (IUD) would be another good option. Or implanon.

I currently use implanon and have not too many dramas with it - last time after DS1 I had spotting for a month about 2 and a bit years after having it in; no problems this time round yet

People brag about the failure rates, but even when not taking it correctly I still didn't manage to get pregnant. Contraception that works when it promises it won't really sucks.

I'm thinking any barrier method would be preferable though: so condoms, diaphragm, that sort of thing. Surgical methods would probably be something to look at if they are finished having children.

It's basically anything without estrogen that's OK. So combined pill and Nuvaring are out, but injections, implants and Mirena are OK because it's only progesterone like the minipill, as are all the non hormone methods: copper IUD, barriers.

I used Mirena after my first and plan to have another inserted after my second. I breastfed from 8mo to 3yo with a Mirena in. The only problem is that they want to be really sure they're not inserting while you're pregnant and prefer to insert during a period. If she's not regular yet it could be hard to time. (However with me they agreed to do a blood pregnancy test instead because I was having 50+ day cycles.)

If she really doesn't like hormones at all, then the copper IUD is more reliable than barriers. (ETA: I guess the minipill means she's OK with hormones!)