She has a mid crushing low sweep that can be done from strings or standalone. Guess what Ryu has? 2H+K and 1P2K (which has no mixup and doesn't crush mids). THAT'S IT
Her 2H+K is only available as is, or with 1PK. Or BT 2K. It's not even considered 'mid-string'.
And Momiji doesn't have that many mix-ups. She may have some, most from her DJ, but they're just 50/50s. Her mix up game isn't scary because you either hold high or mid kick when she's in DJ, or mid P or K when she's in regular stance.
Yeah, Momiji is safe. But a lot of those moves are moves that we don't actually use. Momiji players know better than to even use her P string because of how every variation of each move (all punches) is the same hit level as PPPP (which is high high mid mid).
Although, Momiji players should know better than to even attempt to use strings when playing her because:
(a) She's very much single-hit based
(b) Her strings are ass
(c) Her crushes are amazing.
(d) She lives on stun-launch gameplay.
She's fine as is, but she needs one thing, and that's for her DJ Throw to be an OH to frame trap her opponents if they block Uzukaze K.