You didn’t tell me not to look so I did. But you ask not to pry so I’ll try not to pry, Shy.
Anyhow, I think SL is right on about her feeling she is losing her place. Adults also feel that way often when an in-law moves in. However, rather than talking to her to try to understand, you should rather affirm her place with quality time.
Not wanting to lose your position is not a matter of Midos Tovos. As the Maharal writes, even the greatest Tzadikim did not like being put down. Think about the reaction of the ???? ??? ??? to Yehoshua’s confidential Nevua, and Rabbeinu Hakadosh — of whom it says ???? ??? ???? ????— when Rebbe Chiya told him that Rav Huna Reish Galusa is outside.
Just like no amount of Midos Tovos would cause you to enjoy getting hit, the same goes for becoming insignificant in some way.
Therefore, 1- reaffirm her importance with quality time, and 2- include her in the decision making process. This would avoid jealousy since she is not being brushed aside rather, on the contrary, getting a boost of confidence. Just like you are not jealous of a Kattan since it is through you, make it go through her.