Re: going to a concert:good idea when b-feeding a 3month bab
I think you'd be perfectly fine to get out for an evening. I would pump and store some milk just in case, but also feed her before you go and maybe it won't be needed. You'd probably only need to have about 3 ounces on hand, which shouldn't take long to pump if you do a little each day. And spend some time with your friend so your baby can get to know her a bit ahead of time (I'm guessing you probably do that anyway). Maybe have her over one evening during bedtime hours so she can see your routine if you're concerned about her being able to get baby to sleep.
Like I said, I think you and baby will both be fine, even if she does get a bit restless, but if you find your anxiety about leaving her is outweighing the fun you're having, you can always just leave the concert early.
“We are not put on earth for ourselves, but are placed here for each other. If you are there always for others, then in time of need, someone will be there for you.”