I’ve only been to WDW September-December during very low crowds. I’ve purposefully done this in order to avoid large crowds. I want to go during the spring in 2016, but DH does not want to go at this time, so I’m considering taking DD6 and going with a friend and her DD3. Said friend wants to go during spring break, the week after Easter, because she’s a teacher and that’s more convenient for her. I’ve heard horror stories from visitors during spring break. I’m really concerned that we won’t have a good time during crowd level 10 days every day of the trip. My only saving grace is that I’m a “veteran,” having been multiple times, and I know to keep my expectations low during that week. By the way, the reason I want to travel with a friend is so that we can stay at the Poly and split the cost of the room. Any and all opinions are welcomed and appreciated!
The best thing you can do is have realistic expectations, which it sounds like you do! I have been on 1 days and 10 days and they really are just different kinds of trips. All disney trips are awesome if you have the right attitude 
Rope drop and afternoon breaks will make a world of difference.
We went this year during SB. I think most days ended up being 10s with maybe a 9 thrown in. It was busy but as long as your friend and kids can handle getting up early for RD (which during SB can be as early as 7AM at MK) you’ll be fine. We were out of the park most days by 1PM when it was just getting insane. We’d come back in the evenings for dinners, fireworks, and a few rides generally with our FP+s. If your group can’t make RDs I’d recommend just staying home. After about 10AM the headliners are all 60 minute + waits.
We have gone our last 2 spring breaks and it has been fine. Last year we were there about 2 weeks before Easter which was slightly less crowded than this year, when we were there Wed-Sunday (Sunday was Easter). You just need a really good plan, which includes early mornings, getting out of the park from 12-4ish, good use of FPP’s, and then later evenings in the parks. We have been there in crowd levels 1 to 10. They are all doable, as Len says a good plan is more important than the crowd level. I say go for it if that is the only time she can go. Staying close to MK will be great! 7am EMH sounds early, but it is amazing how much you can do before all the crowds get out of bed!
I have gone to WDW during President’s week as well as Easter/Spring break only in the past (level 9/10 crowds) and on average wait was no longer than 15 min (except 30 min one time for Soarin’ with FP) but this was during the time when the old Fastpass system was in use so I don’t know how to work the new system to its max (esp since I will not be staying at WDW resort so can only reserve FP 30 days in advance and not 60 days in advance). I also had used www.ridemax.com and paid subscription to plan the day in addition to Touring plans for the crowd calendar and general advice, b/c at that time touring plans did not have option to personalize the plan and we were not able to start at rope drop but arrive to park around 9:30 AMish, had early lunch, took afternoon break, had early dinner and back to same park in early evening. This time we plan on going April 2 - 9, 2016 but it’s not a typical spring break week though.