To grow, you've got to get your body anabolic. That doesn't mean take anabolics though. It just means in a growth state.
The best way to that state is to train the entire body. Either by doing a full
body workout 3-4 times a week, or training the whole body, one or two parts at a time to failure, over the course of the week.
Even to make arms grow - you've got to work the legs and back. Don't bother looking for a "glute specific" routine, work the whole body, including the legs and butt.
The exercises I suggested are the ones I'm partial too and the ones I've used specifically to make my butt and hamstrings bigger and stronger.
Lunges are great too, I just can't do them. Another thing, to make squats more butt specific - do them with a wide stance, feet 1.5-2x shoulder
width apart, get your butt as low as possible (you won't get much below parallel this wide though), then drive up through your heels as if you are trying to push the floor apart. This uses the glutes and hams as the prime movers in this lift instead of the quads. It's called a powersquat...you ever seen a powerlifter with a tiny butt? And you never will.
One thing i will reccomend that you don't do is leg curls. These isolate the glutes out of the movement and use hams only. This makes the hamstrings bigger in comparison to the glutes...not your stated goal.
As far as ecto, meso, endo... I don't know or really care about that. I'm not a trainer but do train a lot of ladies around my town. It wasn't intentional, I didn't want to, but they came for help and I couldn't say no to someone who wants to look good in a bikini. It's just my part of making the world a better place by helping improve the view. For men and women, the training principles are pretty much the same. You want to grow - you've got to eat for it.
That means start here:
Calories: 16/lb
Protein: 35% of your calories
Carbs: 45% of your calories
Fat: 20% of your calories
Then adjust up or down based on results. Eat more if you aren't growing, eat less if you are getting fat. It may actually take up to 20 calories/lb to gain for some people.
4 inches in a month is a lofty goal. I've gained 30 pounds in the last 3 months and have only picked up a little over an inch all over my body - a bit more in the chest.
One other thing - you mentioned not wanting to get too muscular? Well, don't worry...women can't do that by accident and most can't do it period without drugs. Hell, most of us men are trying to get too big and can't do it either. See the wormy looking guy in my avatar? That's 3 years of hard training and not even close to big yet.