Ahh, I do understand. It can be so hard! My MIL, whom I love dearly, watches my baby while I work. She plays with him constantly while she is here, I have to elbow her out of the way to get to my baby. I work at home, so I do like to breastfeed when I can, and I like to go to him when he wakes up from his nap. But as soon as he makes a peep, I have to run to his room to be the first one there! When we go to her house, my husband and I, she whisks him away from me and sometimes it makes me mad. I am glad to have help, but since she is my daycare provider, I do think she needs to care for him on my terms. I do pay her a very small amount of money, it's all she will take. If she only saw him a few hours a week, I would not care, but during those days, I do give her direction, and she does listen, sometimes. I have asked her to let him play on his own one time a day, while she folds clothes or eats lunch, and keeps an eye on him to see that he is safe ( he is 12 months and walking) but she does not do it. THIS IS VERY HARD FOR ME, because it makes him so overstimulated, then it is my job to nurse him to sleep, and he doesnt want to go to sleep, hes having too much fun, so is she really helping me???
SO, I have enlisted my husband, and he says he is ok with it, since it is HIS mom, he is going to talk to her about it, and let her know that he too thinks she should give the baby a little down time. I am trying really hard to not talk to her about it, because I believe my husband needs practice talking to his mom about feelings etc, so I am leaving it to him.
One time, we were out to dinner with his family, and I had not been with the baby all day, and I felt like my night job was to drive my baby around to places so his family could be with him. I got to the restaurant and she reached to take him from me, and I held on to him tight and said, actually I am going to hold him tonight. She was shocked, and the whole dinner was so tense because I had expressed my wishes, and I was in a bad mood, which was unusual for them to see. For about 3 weeks after that, he only wanted me. I think that I somehow projected my possessiveness onto him that night. Somehow he saw that MOm was asserting herself and wanted to be with him and she must have a good reason so she must be right!
All that said, you say that you can not talk to her openly about this, but you want to be number one. First of all, you are number one. She really likes to play with grandma, and grandma probably spoils her, grandma does not have to get up in the night, grandma only has 3 months and she is going to spend every SECOND she can with baby, and baby likes it. Our babies can be cranky with us, because they feel safe with us, it doesnt mean they dont want to be with us. If you want her to back off, YOU HAVE TO TALK TO HER. Or get your husband to. Imagine how much easier it would be to talk to your own mom about these things. Well guess what, she IS his own mom, and he can do it. You can probably help him find some kind words to talk to her about it. If it were my husband, I would be ok with whatever he had to say to get it out there - he can call me hormonal, whatever, as long as he talks to her.
The only other thing I can suggest is, sometimes I just make light of it and elbow her out of the way. That might be what she expects. I say "HEY! That's my baby!", and I cutely run over and elbow her out of the way. OR "HEY! I wanna hold my baby" Luckily I have always breastfed, and he doesnt like to take a bottle, so I always have that time with him. Grandma probably thinks she is helping, she knows how hard it is, if you can keep your words coming from your feelings, how can she resist "I want to be with my baby?"