Good news, bad news.

After she hit 49, the MSQ got her about 40% of the way to 50, then dumped another level requirement MSQ quest in the way, this time at 50. So, the MSQ really does leave you experience deficient from 40-50. Additionally, the way it breaks it up, it may be best to grind to high 40's as soon as you hit 39. PotD does make this incredibly fast in comparison to other methods, and if you have HW installed, any exp overshoot is a head start on 50-60.

The good news is that all the content after 2.1 and before 3.x also gives you a head start on 50-60 leveling. She's almost level 51 as she approaches Levi.