Dom and sub are most commonly associated with BDSM, yes, but can also apply just in terms of describing what kind of "energy" partners in a same sex relationship have. I am a lesbian and I tend to be the dominant or "top" but I can go either way so technically I'm a "switch". I just tend to prefer being a top, it just feels a lot more natural to me. *shrug* Sometimes those roles are not obvious and if its not discussed before heading to the bedroom you may find yourself in an awkward situation where both want to top or both want to bottom, lol, and it can be a deal breaker for some.

There are yuri-specific terms for "top" and "bottom" just like in yaoi. Whereas in yaoi the top is "seme" and the bottom is "uke", in yuri the top is called "tachi" and the bottom is "neko". So if you ever read a yuri piece and there's a reference to a cat (neko) or a sword/something stiff (tachi) you're probably seeing a sex pun that doesn't translate well, lol.
So Momo has gone full-tachi. You go girl! lol