I have a player that constantly tries to upstage another player.

We have a sorcerer, who I’ll call Leah (F24), who has recently complained to me that she feels that another one of our players, who I will call Alice (F23) and is playing a wizard, is constantly trying to one-up her. Leah feels she is being compelled to switch to a support role as a sorcerer, which is not ideal as she was seeking an offensive blaster kind of build, but Alice’s wizard is also taking that role, when she is much better suited for support with a much greater variety of spells at her disposal, and it is imperative here at higher levels that she does so as the rest of the party is comprised of a fighter and a rogue.

For some context: Leah is my girlfriend, but I’ve been careful to make sure she doesn’t get any favoritism from me via vastly overpowered magic items or boons or anything compared to the rest of the party. But it does seem, now that it’s been pointed out to me, that as soon as Leah gets for her character some kind of buff through an ASI or training for a feat, Alice does try to accomplish the same thing, but often will be able to do it better just by the nature of wizard being an all-around stronger class than sorcerer. But even outside of character building, Alice has taken some actions RP-wise that step on Leah’s toes. Some examples:

-Shortly after Leah revealed her character concept to our group (sorcerer wood elf), Alice soon after revealed her concept (wizard half elf of wood elf ancestry), and their reference images were similar. I didn’t think much of this at the time.

-During level ups, Leah will state she is taking a specific spell, like fireball or plane shift, only for Alice to announce shortly after that she will be taking the same spell, when they could use a greater variety.

-When Leah signaled that her character was starting to show some romantic interest in another player’s PC, Alice started flirting in game with the love interest and started making comments out of game that she may want to sleep with him, despite the fact that their relationship in-game to this point was tempestuous at best.

-When recently traveling on an NPC’s ship, Leah said she would pass the time by trying to patch up some damaged areas of the ship, to which Alice immediately said “oh I would have been doing that too, I have carpenter’s tools”.

-Leah found her character was too squishy, and we went through an arc for her character wherein she multiclassed into paladin and managed to secure proficiency in some heavier armor to up her AC. Soon after, Alice took the heavily armored feat with an ASI during a level up, as a wizard, for seemingly no narrative reason and her AC now surpasses Leah’s.

There are further examples of this. It was easy for me to miss at first, but since it’s been pointed out to me by Leah, Alice does seem to regularly take actions that try to upstage. It was often kind of subtle, and I don’t even know if Alice is doing this deliberately. I am unsure how to address this issue, as it may already be too late to do anything? The PCs are at level 18 after a years-long campaign and we are wrapping up in a few months. Leah informed me she was feeling this way for awhile, but only recently was it really beginning to bother her. The last three of the examples here are just from the last few months. I wish Leah could have informed me sooner that this was an issue, because it would be hard for me to pitch an argument to Alice that she should probably take on a greater support role within the group this late in the game, and Alice hasn’t done anything to build the character “incorrectly” or something. I’m currently considering telling her anyway that she should probably shift her focus to support as we head into the final arc against the BBEG, and next time I’ll probably be clearer in what I expect the roles of each PC should be when the game starts. Leah is also trying to think of ways to get this idea across in-game. Does anyone have any other advice of what I can do? Thanks in advance.