What lifts/exercises can I recommend to my girlfriend to make her bum bigger? Is there any way to achieve that without her thighs getting big and muscley?

Ps. No neg repping me, she asked me!

Squats are a compound lift that works both the upper and lower body pretty well. 

I had my first ever proper training session (with a trainer) at the gym yesterday. I've been using aerobic and weights machines for many years (intermittently), but after going paleo I thought I'd better use free weights, particularly kettlebells.
All we did were
squats (no extra weight, my 11st was enough),
lunges - 4kg
one-armed row (?) 5kg
single arm kettlebell jerks = 4kg.
One minute of each + one minute rest and then the same thing over again on the other side.
Followed that with a few stretches and I can hardly move today.

If I did that 2 or 3 times a week, would that be a good way to get strong? I'll also do some general recreational exercise such as swimming and walking just to feel good.

I'm 53, female, about 2st overweight (28lbs)

What lifts/exercises can I recommend to my girlfriend to make her bum bigger? Is there any way to achieve that without her thighs getting big and muscley?

Ps. No neg repping me, she asked me!

I think we're going to need to see some pictures in order to make accurate recommendations.