@Popconnection From my experience:
~The pill gained me 10 pounds within a month and I stopped it. I went to the shot which is also just generally more reliable for me since I can’t forget it. Some girls do gain weight from the pill but not exercising doesn’t help that.
~This same situation happened with me and my boyfriend but mine was related to a… temporary depression (not clinically diagnosed but was very effective). I was just having too much trouble with school, friends, and future decisions to focus on my eating and exercising. I didn’t communicate my problems to my boyfriend enough and (from what I can tell) he was afraid to approach the topic. I realized it eventually and am working on getting rid of the weight gain from it. But as I said, I realized it. Sometimes it takes a long time to admit something is really bothering you and to the point of affecting your health. When my boyfriend did decide to jump in and try to get me to exercise more, I didn’t like the direct prodding and made me feel more aware of how I messed up. So he had to do it circuitously. I admit that ideally he shouldn’t have to do that but it’s a sensitive topic for me and it’s one of the few irrational things I’ve got.
SO, my advice is this:
a) It could be the birth control and being too busy at work decreases exercise time. If she’s unhappy with the pill, she’ll change to something else. I recommend the shot if she takes a multivitamin.
b) It could be due to stress or depression. If you see her looking down or staring off into space, poke her. Check to make sure everything’s ok. A good way to relieve stress is to work out physically, so you could recommend it to her that way if she’s stressing.
c) She probably does realize it’s happening but doesn’t know how to approach fixing whatever the problem is. You could try the direct approach. But I give no guarantees about how it will go. You’d know your girl better to know if weight is a sensitive topic.
d) Doing it circuitously worked for me. My boyfriend goes out on a lot of bike rides and it makes me want to bike more. You could also look into gyms that have many different types of workout areas. When my boyfriend and I go to the gym, I actually don’t like sticking together because I like working at my own pace, but I like that we’re both there at the same time. There’s also creative recreation like indoor rock climbing and team sports that you could look into. ( @Cruiser ‘s recommendation about hiking was pretty good.) I’m a big fan of taking walks together and finding new things.
e) Start getting the food in the house more healthy. If you live together or eat together regularly, tell her you’re getting into a health kick and want to green things up a bit. (More veggies, more meat, browner grains, fewer sweets, etc.)
One thing my mom does if she wants to lose weight is make everyone else go on the same diets or exercise things as her. While it’s frustrating, you could ask her to go on the same regiments you do to help you lose weight and trim up. “her doing it with you makes it easier to focus on and stick to. Supports you, etc.”