you have to remember to her, her baby has announced she is pregnant, that's a strain on any mother, especially when to her your still young, still a child in her eyes. To add to that pressure, she probably feels like she's loosing you, not only to your boyfriend, but to his family too. Her automated response is probably not the best one because it's pushing you further that way but it's also natural. Talk to her about how she's on and off and how it makes you feel, and respond to her. opening up should invite her in to your life that she feels she's missing out on, while solving it to, and strengthening your bond. Hope this advice helps, best of luck.
Well I never been in that situation but I don't want you to be stressing about it I'm sure she loves you may not like the situation but maybe she is still not use to her baby girl being pregnant but I really think you would tell her exactly how you feel cause your going to need her and vise versa IM not an expert but in do wish you the best.