Go and ask your GP if it is ok, rather than relying on 2nd hand advice from a friend. I know plenty of breast feeding mums who run, with no issues like you describe. I had a prolapse after giving birth to my daughter, nowt to do with running, I was unlucky. Fortunately it is much improved after lots of Pilates and I now have no problems with this and running.
I personally found 17 weeks post birth too soon to be running again, but again, I know lots of mums that have run from earlier than that. If you've been doing bootcamp without problems I would expect that some gentle running would be ok, but do give yourself lots of time to build up slowly. One thing to bear in mind with all exercise and breastfeeding is that all the hormones do make all your ligaments etc more flexible than usual, so you should take things carefully so as not to get injured.
Get her to take a look at the Freya Sports Crop Top. The sizing can be a bit odd, so she'd need to try a couple on maybe to find the right fit (Less bounce give great advice over the phone and have good returns - and actually may be able to advise on what else could work), it's the only vaguely comfortable sports bra I have ever had, and it works.